When you say all Mega Man, I'm assuming you mean the original series. Because the Mega Man X games and the Battle Network games have lots of forgettable tunes. As for Wipeout, DEFINITELY. I'm not a huge fan of those games, so I mainly use those PS1 games as cd's (since you can just put them in a regular cd player and listen to the soundtrack... I do that with the game NITROUS OXIDE too).
I gotta say, the BEST game music of all time has to be by Yuzo Koshiro.. Also, the best game music, in my opinion, was definitely on the Genesis. Some completely weirdass sounds they got out of that thing. Anyone ever heard of/played the game Biohard Battle? Just insane Genesis sound card bass!
Here's "the music of video games" video with Journey to Silius..
http://www.youtube.com/watch?v=PBM-m82Za_0
They absolutely pushed the NES's sound card to its limits for it.