Such a difficult question as there are sooooo many cool games
If you look at this thread you can see all the games that I've currently setup in WinUAE (warning; over 1400+):
http://eab.abime.net/showthread.php?t=80841
Reverse 2 years back and I had only added around 500 games; these were probably all the must haves IMHO
Anyway, when I get home tonight I'll put the list of 500 here