1. Evil Zone
An amazingly simple yet enjoyable game, especially with it's mock-tv style story mode. The story mode would give you a cutscene before and after each fight, and then a voiced slideshow ending. Yuke's managed to make a good moveset for each character depending on d-pad and triangle button combos you could press. Evil Zone is practically a cult classic. If you ever get the chance to pick this game up in good condition, I highly recommend it.
2. Marvel vs. Capcom 2: New Age of Heroes
What is there to say about one of Capcom's biggest fighters? All favorites from the vs series return on both sides, alongside some new Capcom characters and some lesser known Marvel characters. The 3 on 3 tag style and frantic matches truly made MvC2 the legend it is today.
3. Street Fighter Alpha 2
Certainly one of the most memorable Street Fighter games. Not only did it debut the wildly popular Sakura, but also made use of Final Fight characters such as Rolent(o) and Sodom (I'm not joking, that's his name). Akuma was even made fully playable for the first time. It also has the better versions of some character themes. Definitely worth picking up by itself or in SF Alpha Anthology.
4. Mortal Kombat Trilogy
The definitive version of Mortal Kombat 3, it also brought back classic characters, and even MK2 versions of some. It also retained nearly all of the fatalities from 3 and up, including the newer animalities and brutalities. Classic stages and bgm's on top of all else made this game a complete package for any MK fan.
5. Tekken 3
The 3rd game of the classic 3D franchise. It really helped to switch gears for the series, as it introduced enough new characters yet kept enough classics that the roster was a near perfect balance. It also had it's cool extras like the ending theater, and Tekken (volley)Ball.
6. Soulcalibur II
Maybe it's just me, but somehow this entry in the series still seems more fun than the others. The solid gameplay and orchestral music really put you in the action. It also featured playable guest characters depending on your system, something still uncommon at the time.