Well one game I HIGHLY suggest if you ever get Gens (genesis emulator) is PowerBall, now that's a damn classic, along with General Chaos.
In terms of Mame games, I'd have to say Super Gem Fighter Mini Mix is a good one, Vampire Savior or Vampire Savior II are very fun, Marvel vs Street Fighter is probably the most balanced Vs game, a VERY VERY good shooter that seems to go unheard of in a lot of game lists is Guwange, which I believe is one of Cave's shooters, and is VERY good, I highly suggest trying that out. Remember mame isn't the only emulator out there for party gamers.
If you're worried about your CPu hindering your performance or more graphically intense fighting games like Marvel vs Capcom, the newest version of Nebula runs absolutely smooth as hell on my 333mhz celeron, you can find a link from
http://cps2shock.retrogames.com It also supports Neo Geo games, and at a 700mhz processor they should all work perfectly, although I'd use NeoRageX just cause that's the smoothest Neo Geo emulator out there.
If you get Snes9X or ZSnes, I suggest getting Megaman Soccer, very fun. If you're worried about your CPU speed in Mame, NBA Jam TE for Snes runs full speed on my 333mhz for the SNES, so that's a good alternative.
-Good Luck, if I find any other games I think you should try out, I'll definitely list em
-CthulhuLuke