This is a fun topic! Sure, Smash Bros., Zelda, Final Fantasy, etc., are great and all, but I think I'll name some lesser known titles(If you've played them then great!)
Number 5: Pokemon Puzzle League(N64)
WTF? POKEMON? LOLZ. Maybe not as unknown as other titles in this list, this game was actually MUCH more fun than you could imagine, even if it is based on pokemon. I could never beat Mewto at the end though. Too hard.
Number 4: The Unholy War(PS)
Although I never beat the main single player game, (I used cheat codes to unlock all characters XD) I enjoyed playing this game's multiplayer battles with a friend. Yes, it was a strategy game, you could just play straight out battles with a friend. There were two sides, the "Animal" side and "Machine" side with different "unit" characters. Each "unit" character was unique and could engage in one-on-one battles with each other. In short, LOVED the 2-player!
Number 3: Brigandine(PS)
This game, as far as I know, has received terrible reviews. I actually like this game A LOT. Tons of strategy in the game. Every 10 levels each unit can "upgrade" into a better one. Each "commander" can control up to 5 units each. There are 7 different kingdom's(i think) in the land(you control one of them) and battle your way for control of the continent(well, mainly to stop the 7th evil kingdom). Kind of reminds me of Dragon Force for the Sega Saturn.
Number 2: Team Buddies(PS)
LOL. First impressions aren't everything, so if you're looking at this box art and saying "WTF is that?" then I understand. A very fun RTS(you can probably tell at this point I like strategy games XD). Control your "Team Buddies" and blast the crap out of opposing teams by using mysterious crates that fall out of the sky. Crates contain weapons; Combining crates equal bigger, better weapons, the biggest being a tank of some sort. All this while protecting your "home base." You've even got different "buddies" like the ninja and cyborg buddies! Trust me, this game is EXTREME FUN!!! MULTIPLAYER IS A GUARANTEED BLAST!!!
Number 1: Tales Of Destiny II/Tales Of Eternia(PS)
Yes, I enjoyed Tales Of Symphonia, like many people here, however I enjoyed this predecessor of sorts by far. Known as Tales of Eternia in Japan and not to be confused with Tales Of Destiny 2, also in Japan, this was the first "Tales" game that I had ever played. One battle, and I was instantly hooked. I enjoy the Tales' series battle system A LOT. If you were stuck, you could press the triangle button and get a little animated scene with those character portrait boxes a la Tales Of Symphonia. Only, these scenes had VOICE, not just static images of characters talking. The game was lengthy too(THREE DISCS). To top it off, MINI GAMES!, my favorite being a card game that you could play anywhere as long as you had it in your inventory. There's a lot of sidequests too. HIGHLY RECOMMENDED!!!
Honorable mentions(since I can only have 5): Survival Kids(GBC) Mischief Makers(N64) Goemon's Great Advemture(N64) Dragon Force(Sega Saturn) Star Ocean: The Second Story(PS)