The fascination King's Gambit by Thomas Johansson is a fascinating book.
King's Gambit: Book suggestions?

I have the The King's Gambit for the Creative aggressor by Thomas Johansson, it is bad. Really bad. The navigation from one variation to another is quite confusing with long streams of variations and games inserted on whim. No hint at what the critical variations are, or the ones that are necessary to know by heart. The guy isn't even a master (which might even be okay if the book wasn't so terrible).
I would recommend not playing the king's gambit, black gets a fine game after a combination of ...d5 and ...exf4. If he isn't playing that then he probably is trying for an advantage!

Joe Gallagher is well known and respected. I've seen many of his KG games. But I haven't read his book on the KG. I heard it is the best. But I don't know.

Neil McDonald's King's Gambit: A Modern View of a Swashbuckling Opening came out after Gallagher's, and is probably more up-to-date. I don't have Johansson's books, but he has a reputation as a very passionate analyst, and can be found posting as Taljechin on chesspub forum.

I haven't read the book suggested by rigamagician but Neil McDonald is a great author. I have read atleast 3 of his books, one of which was how to play against 1. e4 with the French. GREAT book!!
I think I'm going to give Neil's Kings Gambit book a try myslef :)

IM David Pruess is big on the King's Gambit. Maybe asking him his opinion on some books would be helpful too. Just my two cents.
-Mark

I had a similar question recently and searched for McDonald's book. It is out of print and quite expensive second hand. However, I managed to find a pdf of the book freely available on the internet. If the OP gets in touch I can send it to him. I haven't managed to read it recently so can't comment on its contents, but McDonald is a good writer.
Quality Chess is supposed to be publishing a book on the King's Gambit early in 2011.

I think "King's Gambit" by Viktor Korchnoi & Vladimir Zak is quite fine! It's even got analysis of some more or less well-known sidelines that are considered slightly inferior for White by theory! And that includes some Muzio gambits as well! Great fun!
On the other hand, here's a counter-question: any (good) books on the Bishop's Gambit that you know of?

The Fascinating King's Gambit by Thomas Johansson mentioned by the original poster is on the King's Bishop's Gambit.

Umm, I here is my stuff again, I must have posted it way back when:
<Bottom right = Paul Keres' book on the KG>

Johansson is most thorough. His The King's Gambit For The Creative Aggressor deals exclusively with 3.Nf3, while The Fascinating King's Gambit is centered on 3.Bc4 only. Johansson is a practitioner of the opening, you can feel the enthusiasm.
Korchnoi and Zak do everything to convince you that the KG is a dubious opening. This is a book from another era, when chess books were thin, chess book covers sucked, and it was enough to get a super GM name on the cover to sell a book. Korchnoi doesn't even play the KG, and it shows.
Missing from the collection - McDonald's book. I was permanently discouraged from buying it by the following amazon.com review:
Overall, this book is a failure to me because it is incomplete and much of the material is derivative. Several key lines are simply not covered, apparently deferring to Joe Gallagher's 1993 work, Winning With the King's Gambit. McDonald's book is merely an update of what has been happening in the KG in the intervening years since WWTKG was published and I would like to have seen more original analysis like Gallagher's book had. Unlike Gallagher, who plays the KG almost exclusively against 1...e5, McDonald seems to have essayed the opening only rarely -- my database shows only nine tournament KG games from 1991 to 1998. To be fair, I did like McDonald's treatment in some lines, particularly the Falkbeer Counter-Gambit. His analysis there is clearer than in the Gallagher book. I can recommend this book only to those who MUST HAVE every book on the KG. For those looking for more up to date info (and interesting ideas!) I wholeheartedly recommend Thomas Johansson's, The King's Gambit for the Creative Aggressor.

Search the database for games from the 19th century go get a feeling.
After that check the C30-39 victories from Bronstein and Short.

I have King's Gambit (Korchnoi & Zak) and The King's Gambit as White (Christiansen, Maser, & Raingruber).
I have a very low opinion of #1. They do no more than summarize comments and analysis by other players without regard for correctness. My copy is littered with my own notes (OTB 1900-ish, CC expert, all of my analysis done pre-engine) on game-losing lines the authors state are equal or better for White. Useful when I got it for an overview of the KG, despite missing numerous variations (including a few important ones) but with resources on the internet this book is now of no value at all.
My complaints about #2 are similar. It too is littered with my warning notes about losing lines in their analysis. Also missing noteworthy variations. It has one element that I valued: a modest compendium of 'bad' moves, presented as end-of-chapter problems with solutions. I haven't seen this in other opening books.
Neither book should be trusted. Analysis is non-existent in #1 and superficial in #2. Of some value for historical content.

The new KG book by John Shaw from Quality Chess should be out by now...
http://www.qualitychess.co.uk/products/1/124/the_king
I want to learn the King's Gambit via books. Which are the best (by experience?) as in easy to read, sound (!), and overall inspiring. Basically, I want to, by the time I turn the last page, feel like playing the King's Gambit without any opening holes and the confidence of winning.
some choices I've found:
The King's Gambit for the Creative aggressor by Thomas Johansson
The Fascinating King's Gambit by Thomas Johansson (While I am more "familiar" wiht the kjng's knight gambit, I wouldn't mind learning the bishop gambit instead should this turn out to be a good opening)
winning with the king's gambit by Joe gallagher
Thanks :)