I'm sure you've at least heard of it, but Modern Chess Openings, 15th edition is very thorough. It's goes into detail concerning all popular openings and their more less popular variations and lines.
Any gambit compilation books?

I used to have MCO 11th Ed. decades ago! (& very useful it was too) I like to buy books on specific openings though, for the chat & extra detail, also humorous chess books.

There is Boris Alterman's "The Alterman Gambit Guide: The White Gambits" from 2010. It includes chapters on the Danish Gambit, the Urusov Gambit, the Philidor, the Cochrane Gambit, the Morphy Attack and many more.

There is Boris Alterman's "The Alterman Gambit Guide: The White Gambits" from 2010. It includes chapters on the Danish Gambit, the Urusov Gambit, the Philidor, the Cochrane Gambit, the Morphy Attack and many more.
I have this book, it's quite good.

check Amazon......for example....
Grandmaster Gambits 1e4 by Richard Palliser & Simon Williams
Alterman Gambit Guide by Boris Alterman (3 volumes)
A site devoted to gambits: http://www.ianchessgambits.com/

I'm specifically looking for a good book on the Evans Gambit. If someone who plays the Evans could recommend one that they have read and enjoyed I would be most grateful.
Yes. Search 'Evans' in this article.....lots of books treating the Evans Gambit.....
Good Chess Openings Books For Beginners and Beyond...
https://www.chess.com/blog/RussBell/good-chess-openings-books-for-beginners-and-beyond
https://www.chess.com/blog/RussBell

Didn't realize there was a book version of "GM Gambits" by Palliser/Williams! (I've watched some of GingerGM's vids promoting it) I'll check out Alterman's series of books too & pick the most suitable/interesting.

As @RussBell mentioned above, there is the Alterman Gambit Guide, published by Quality Chess. There are three volumes — one for white gambits, and two for black gambits. Everyman also published a two volume set called The Gambiteer I and II, by Nigel Davies. And for historical context, there is The Gambit, by M. Yudovich, published in English in 1989.

Gambits (1982) by Yakov Estrin
Contains 23 chapters of selected gambits. Includes dozens of games and game fragments, with commentary...
https://www.amazon.com/Gambits-Yakov-B-Estrin/dp/0931462207/ref=sr_1_1?crid=1ROUW7U10M91I&keywords=gambits+yakov+estrin&qid=1658445372&s=books&sprefix=gambits+yakov+estrin%2Cstripbooks%2C128&sr=1-1
the book is available for download on Scribd and PdfDrive....
https://www.scribd.com/document/396115901/Estrin-Gambits-1982
https://www.pdfdrive.com/gambits-1983-06-e191979775.html
Both sites are safe. I have downloaded dozens of chess books from both sites over the years...
https://www.chess.com/blog/RussBell/scribd-com-for-online-chess-book-reading
several pages from the book which I downloaded from PdfDrive.....including the entire table of contents...

You might want to check out various issue of the Unorthodox openings newsletter
http://www.unorthodoxchessopenings.com/
there is plenty of gambit coverage in each issue, they are up to issue 39, downloadable for free.
I wonder, have there been any such books published? You'd think such a book would sell like hotcakes! I once bought a humorous book called "Unorthodox Openings" by Benjamin/Schiller, which was (and still is) a good read and inspiration to occasionally dabble in wonky openings. The only drawback is that the more playable openings were covered too sketchily and it was generally quite a slim book - could have been double it's size.
Also, where best to find up-to-date books about specific gambits or slightly off-beat openings, especially Blackmar-Diemer G., Milner-Barry G., Morra G., Dutch, Bird's O., (any books on the Tayler Opening lol?)

PS- I already have Esserman's book on Morra, Simon Williams book on Dutch (prob. a bit out-of-date now) and a very outdated book on BDG by Gary Lane, which contains at least 1 crucial theoretical flaw (written before computers helped with checking lines).