Ng5 is typically marked with a ?! now adays simply because there are good counters for it.
If you're in love with tactics why not do a gambit?
King's gambit w/ 1. e4 e5 2. f4
However, I prefer a vienna game, the opening line for which is 1. e4 e5 2. Nc3 which allows for f4 to be played later but w/ more developement before hand and less crazy opening lines to memorize.
If you want tactical games, the Ruy Lopez gives you a lot of chances, but always keep in mind that openings are most of the time positional as well: who gets the center? From the center, you can make tactical attacks! The tactical spirit may help to try a gambit (King´s gambit, Danish gambit), where you get most of the time a lot of space to attack for the pawn(s) you have given.
That´s my opinion, perhaps you don´t agree on it...
Assuming your primary goal is learning the game rather than winning every game I would suggest you choose an opening that encourages you to grow positionally. If you choose to only be a tactical chess player then you are choosing to be only half a chess player...position is much more important than tactics and you need to stretch yourself to learn more about it. The common saying "I'm a tactical player rather than a positional player" or vice versa is an amateur mindset, although it sounds sexy.
I'd avoid Ruy Lopez simply because there's so much theory and positioning about it.
That's exactly why I personally avoid it now as white and instead play an Italian Game after 1. e4 e5 2. Nf3 Nc6 and rather than Bb5 for the lopez I prefer Bc4 and it's attacking options.
Well after the Ruy Lopez you get a lot of attack at the e5-pawn, and after a Nxe5 you got your knight in the center, ready to castle and bring your rook in, and let the knigside attack begin! (Then try the Tactics Trainer, you get a lot of kingside attacks)
I like the scotch, if you want tactics try the scotch gambit, if you upgrade to diamond for a month, there are some videos on the scotch gambit, alternatively,
http://www.chess.com/groups/view/the-scotch-fans-team
i vote for the scotch game. one of my favorite openings. i especially like the goring gambit - 1. e4 e5 2. Nf3 Nc6 3. d4 exd4 4. c3 which is normally followed by 4...dxc3 5. Nxc3. then you can still place your bishop on c4 as in the italian and you have a nice open, tactical game.
Stick with the Italian. I'm not sure how you're playing the GP, but from the way you describe it, I assume 4.c3 5.d4. If that seems a little slow to you, you can force the action a move earlier with 4.b4, the Evans Gambit. That should satisfy the attacker in you. Even declined, it gives plenty of aggressive opportunity.
Black can't avoid it sooner than that and still be in an Italian.
Against the 2K, either Ng5 (which, contrary to what someone above said, most certainly does not have a "?" appended in any reasonale monograph on the opening) or the modern mainline with 4.d4 exd4 5.e5...
As far as opponents getting counterplay, that's not the opening's fault. That's just the nature of chess as you move up the ladder.
(Hard to go wrong with the Scotch or KG, either.)
Thanks for all the replies, guys. A lot to think about there. The Vienna game looks really interesting to be honest, and I think i'll spend some time reading up on it in the near future. So thanks. :)
And I do agree that I need to improve positionally, and I believe I have done so unwittingly in the last 6 months. :P I do, however, have a lot more fun when playing tactically rich games. And mostly I like having fun whilst playing. And, of course, when I feel I can no longer improve I will spend some time improving my positional chess.
And as for the Ruy Lopez: I have spent some time looking at the position after 3... a6 from Black's point of view and found it largely fun, but as for all of different variations after Black's third move I got lost and my head almost blew up from information overload.
And continuing with the Italian game in the Vienna after 1. e4 e5 2. Nf3 Nc6 makes the Vienna an even better option for what to study next. :)
Stick with the Italian. I'm not sure how you're playing the GP, but from the way you describe it, I assume 4.c3 5.d4. If that seems a little slow to you, you can force the action a move earlier with 4.b4, the Evans Gambit. That should satisfy the attacker in you. Even declined, it gives plenty of aggressive opportunity.
Black can't avoid it sooner than that and still be in an Italian.
Against the 2K, either Ng5 (which, contrary to what someone above said, most certainly does not have a "?" appended in any reasonale monograph on the opening) or the modern mainline with 4.d4 exd4 5.e5...
As far as opponents getting counterplay, that's not the opening's fault. That's just the nature of chess as you move up the ladder.
(Hard to go wrong with the Scotch or KG, either.)
Sorry, started writing my previous post before your reply.
I usually play 4.c3 5.d4 but have recently tried at least one game with Evans gambit. I lost some momentum and now the extra pawn he has could make some difference if we reach an end game. I do still have some attacking options available to me in that game and have a few lines of attack planned. :D
I might try a few more Evans gambit games and see how I find them.
trigs: That Goring gambit looks scary! though after 6. Bc4 and a 7. Qc3 it could be quite interesting indeed.
evan's gambit is amazing. sadly, it rarely happens as many do not play Bc5 (and instead opt for Nf6 for the three knights variation).
I play evan's whenever I can. It makes things more exciting 
. I used to play Greco Piano as opposed to Evan's but I've since seen the "error" in my ways
2. Ke2.
I recommend the Scotch Game for an opening that avoids loads of theory while giving lots of opportunity to a tactical, aggressive player. I have had lots of trouble against the Scotch from the Black side in my life, although theoretically Black is supposed to be able to equalize without too much trouble. But don't dismiss openings because with best play they lead to equality: the compensation may be not having to learn myriad variations of "superior" openings.
The Spanish game can get extremely positional.
So I don't think it's the best fit for you.
And while I am sure you would like some of the other tactical suggestions given to you already, they all come with one drawback.
And that is that you would have to give up all of the Piano knowledge that you have learned.
I have played the Giuoco Piano all of my life.
And I can't imagine playing chess without it.
The tactics are gorgeous, and every game I play with it seems to be thrilling.
But a while back, I had the same question that you are having right now.
What do I do when Black responds with 3 ...Nf6 instead of 3 ...Bc5?
The move 4 Ng5!? certainly gets mixed reviews from the peanut galley.
But it has what you and I are looking for!
Tactics, tactics, tactics.
The games tend to have a similar feel to the Piano, so you will feel right at home.
And the studying and playing of the Two-Knights is extremely rewarding.
The games are exciting and very much fun.
If you obtain a better understanding of the openings than your opponent does, you will often sweep him off the board with a brilliant early victory.
And the best thing is that by learning the Two-Knights, you do not have to give up everything you learned in the Giuoco Piano.
You will be adding to your opening knowledge instead of simply replacing it.
By preparing both into your repetoire, you will be ready to fight against a wide range of opponents.
Good luck!
--CM
I recommend the Scotch Game for an opening that avoids loads of theory while giving lots of opportunity to a tactical, aggressive player. I have had lots of trouble against the Scotch from the Black side in my life, although theoretically Black is supposed to be able to equalize without too much trouble. But don't dismiss openings because with best play they lead to equality: the compensation may be not having to learn myriad variations of "superior" openings.
The Scotch was out of favor for many years, but Gary Kasparov has said he considers the Scotch, like the Ruy Lopez, a serious try for a lasting advantage. I dont know how many of the current super grandmasters agree with him, but it has seen play at the very highest levels of competition.
Back the Original Poster: do you play live (otb) or correspondance? I find that correspondance chess is a great place to try out new openings, because it is 100% kosher to look up theory when you are playing turn-based. If you want to give a more complex system, like the Spanish, a try, a correspondance game might be the way to go. You have lots of time to examine the positions that arise, and you can consult databases, MCO, etc, to see what is often played in master level games. It's a way to get your feet wet on a opening without having to feel like you are "booked up" before you sit down to play it.
I have been playing chess for about nine months now, and I have been doing ok playing the Italian and hoping to get into a Giuoco Piano. This is my prefered opening as white and I have spent quite some time analysing it.
I feel though, as I am progressing and I am able to hold my own against better and better players that I either don't reach the Giuoco Piano or that my opponent knows how to gain counter play. I especially get upset when it turns into Italian Game: Two knights defence - though I might start playing Ng5 if this arises again.
I was thinking it is about time that I spend some time studying a new Open Game opening, whether it be the Ruy Lopez or the Scotch game or even something else.
As I am more a tactical player and I feel I only have a small amount of positional sense I am more willing to open with e4. I actually dislike the d4 positional games although I don't fare too badly against d4 as Black.
So my question is: What continuation do you think I should study next? Keeping in mind that I do like tactically rich games and that I am quite poor positionally.