In no particular order...
Half-Life 2 & Episodes 1 & 2
I don't usually like shooting games, but HL2 is different. The story and visuals are amazing to me, and the Gravity gun is so much fun to use. I don't know what it is about this game, but I love it.
Final Fantasy VII
It was the first Final Fantasy I ever played, and it's my favourite to this day. Awesome story, music and battle system. I just wish I played it more often.
Breath of Fire III
I think this might have been my first RPG, I'm not sure. I absolutely love this, everything about it screams epic. It may not be much, but it's one of my favourite games of all time. It's a shame they didn't do more than just a port with the PSP version, it would have been nice for extra things, like side quests and minor character development, oh, and more endings. That hardly bothers me though.
Portal
Ahh... Portal. It's so much fun, and some parts in it are hilarious. It sounds silly but I think I like the actual puzzle solving less than actually escaping from the place/getting to the last area. I wish they'd have made that part longer. But yeah, it's bags of fun.
Tales of Symphonia
I find ToS really fun, but the storyline is kind of wank. But it does pick up eventually. With all the new techs and characters, the battle system never seems to get old. Oh yeah, and the music. I love the music a lot, the battle themes get you so hyped up.
Oddworld: Abe's Exoddus
Had to have an Oddworld game on here. I get loads of nostalgia whenever I play it. Still, to this day I sit in awe at how pretty everything looks, mainly the level backgrounds. I don't play it much, but when I do, I enjoy it.
Quiksave gets the best of me.
The Legend of Zelda: Ocarina of Time
The game is an absolute masterpiece, the story, gameplay, music, dungeon design etc. I would gladly play it multiple times in a row. I can't really find a fault with it, however, Young Link ought to have more screen time, the game was more fun as him IMO.
Sonic 3 & Knuckles
S3K might just be my oldest favourite game. It has one of the best soundtracks I've ever heard, and its the longest classic Sonic game, that being a bonus of course. I like to play it every now and then, but it never takes me as long as it used to, though.
Chrono Trigger
I love Chrono Trigger. I think I could say I prefer the story to anything else. I've mentioned it before, but I'm keen on apocalyptic events. (Fiction obviously, it would be sick if I found thrill in them in real life.) Also, the music is win. The battle system... eh, not too great but it's pretty fun.
Tomb Raider 3
My first/most played Tomb Raider game from when I was a kid. Best music, locations and voice actress for Lara out of all the Tomb Raider games. People dislike it because it doesn't have many tombs, but I don't care. The levels are still great and can be explored, who cares if they're not dull tombs?