assuming you're just talking about video games and not also card/board games etc.
i just listed these. they're not ranked. i put a reason for why they're on the list in parentheses
1.warcraft 3 (the best role playing strategy game, and easiest to make minigames out of that i've tried with)
2.starcraft (the best real time strategy game)
3.final fantasy ix (final fantasy game with very good music and fun restrictive system)
4.final fantasy vii (one of the better final fantasy titles. very good, lots of flavor)
5.saga frontier ( the best rpg ever. everything is great about it)
6.civilization (the most influential turn base strategy game and very educational as well)
7.master of orion (the best turn based strategy game ever)
8.street fighter alpha 3 (had a very cool fighter customize system, very nice)
9.tekken 4 (had some really good level design for a fighting game, plus had replays)
10.space wars (a game that is really old and i don't have access to anymore)
11.hostile takeover (my favorite turn based strategy game, anyone have the sequel?)
12. worms (sortof a copy-cat of scorched earth with a twist toward lemmings?? Humorous and fun)
13. scorched earth (a tank style turn based strategy game...or is it a turn based shooting game? or what kinda game is it again? i'm not sure)
14. lufia 2 (best nintendo rpg that i've played, puzzles and drama, and a special 100 floor dungeon
15. final fantasy first for nintendo (4 chaos and garland etc) (great music, lots of drama)
16. ultimate mortal kombat (fantastic style fighting game)
17. rival schools (very very very very intesrsting fighting game. love the high school characters)
18. pokemon game boy game (any version, craziest coolest rpg around, but nowhere near as epic as saga frontier and not as homey as dewprism)
19. ffx-2 (an extremely creative game. great music including songs you HATE. international version is better than the first one and lets you play with other than the 3 main battle members. main thing i don't really like about it is that it flashes around the prettiness of the main characters so much. if you can get past that, this game rises above all other ff games. only thing it's missing is a freaking checklist for your 100 percent to complete the game! lol...)
20. saga frontier 2. (lots of fun story but not much else. good battling system but underdeveloped throughout the game. game overall seems too little effort put into it. fantastic music and the story is great too. not really even an rpg but a spg, story playing game.)
21. command and conquer tiberian sun. (this game has some cool ideas. never got around to trying the newer stuff but i don't know about all that C&C stuff...the different discs not playing on some OS really is aggravating. if C&C were more user friendly it would be a great game.)
22. mortal kombat 3D (still waiting for the ultimate mortal kombat 3D though...)
23 dewprism/threads of fate (one of the funniest and fun rpg games around)
24 star wars masters of teras kasi and jedi power battles (two best SW games)
25. pokemon puzzle league (songs from the soundtrack, and this game is even better than tetris!!!)