In no particular order:
Pokemon Silver-GB - Johto is my favorite region to travel. This one of my first Pokemon games (Gold). If the built in clock hadn't killed the save batter, I'd still be playing it now. I am more excited about HGSS than even Generation V because of this nostalgia.
Champions of Norrath-PS2 This is a classic RPG by Sony. You can be a Warrior, Elf, Paladin, Mage, or Dark Elf. It doesn't really matter who you choose. It is just your preference. I liked this game so much, I couldn't sleep because I couldn't stop thinking about it.
Metroid Zero Mission-GBA A remake of the classic NES game Metroid. This was the first Metroid game I have ever beaten. I still play it tons. I am excited for Other M when it comes out.
Super Mario Land 2: 6 Golden Coins-GB This was my favorite Gameboy before I was introduced to Pokemon. It's a classic Mario game, but it was the only one I owned that had upgrades further than Fire Flower. I loved collecting the coins, but I never got around to beating the game. I could probably now since it's been about eight years. I like this more than the original Super Marios Bros. mainly for nostalgic reasons. I always played Gameboy more than our NES, so I had more fun playing the Super Mario Lands.
The Legend of Zelda Twilight Princess-Wii This is my favorite Zelda game out there. The graphics were gorgeous, the sidequests were entertaining, and the plot was fascinating. It was even a super long game to get through. It took me about 37 hours (I don't remember exactly) without collecting all of the heart pieces, Poes, and whatnot. BY far one of the hardest games I've played.
Midnight Club 3-PS2 This is my favorite racing game to date. It surpassed Need for Speed in the elements of customizing the car, how the races were held, and the clubs. I like how the races are held in Midnight Club 3 more because of their freedom. Instead of going on a set track, you choose how you get to the finish. With the exception of a few race modes, you just drove however you wanted toward the next yellow flares that eventually led to a red flare which signified the end. The game also had clubs where only a certain type of car was allowed to participate in the races held there, for example, muscle cars. When you got far enough through these clubs, you got upgrades to that type of care (like rims). Midnight Club 3 changed the way I view racing games.
Medal of Honor Frontline-PS2 In my opinion, this series is superior to the WWII Call of Duty games. This is one of my favorite shooters because it basically started the WWII saga of first person shooters (if I remember right). The game starts out with D-Day and you have to take out the nests while guarding certain key members of your squadron. This is one of the games that really got me into first person shooters.
Gun-PS2 Another one of my favorite shooters. This game takes place in the Old West. I remember watching my father play this years ago and I couldn't wait to try it (it's M so I wasn't allowed to play, only watch) Now that I'm finally old enough, I love this game even more. The game's tutorial is even fun to play. You try out the gun controls by hunting. The tutorial didn't even diverge from the storyline like most tutorials do. You actually hunted with your father to make money. Gun is and will always be my favorite Western game.
Super Smash Bros. Melee-GCN The best multiplayer game of all time. This is the main reason I wanted a Gamecube for my birthday. I wasn't into Metroid or The Legend of Zelda back then, so I had no other motive. The action is sweet, the controls are slick, and the player selection was amazing. The reason I chose this over Brawl is the lag in Brawl. I can play so much easier in Melee because the lag. Characters seemed slower in Brawl. Brawl does have the greatest player selection though.
Guitar Hero III-Wii Even though real guitar is more fun to play, I still love this game. I've only plyaed Guitar Hero Rocks the 80's, Guitar Hero World Tour, and Guitar Hero Van Halen other than this and this is my favorite. The main reason I like this more than the newer World Tour is because of the setlist. I find the songs on III more entertaining to play like Cliffs of Dover, One, Paranoid, etc. I have never played band mode on Guitar Hero World Tour, so I am no considering that in my choice for this.
I also can't believe I came up with ten games. I am an impulse game buyer based on reviews and whatnot. If I hear a game is good, I'll research it and see if that person was alone in making that decision, or most people agree. I also research the game that was most liked by people if I'm new to a series so that I don't choose a bad one and have a bad first impression.