I decided to make a list of my favourite video games and post them up here so here is my list (with links) in no particular order;
Duke Nukem 3D http://en.wikipedia.org/wiki/Duke_Nukem_3D
Basically my favourite game. Runs on the Build Engine and is a must have to play. You can buy from GOG.com.
Another one of my favourite shooters. Has a old western theme and runs on the Jedi Engine (Dark Forces). You can no longer buy the game so try on eBay.
Sonic 3 & Knuckles http://en.wikipedia.org/wiki/Sonic_&_Knuckles
My favourite Sonic game as it's lengthy and fun to play. The special stages are my favourite from any Sonic. You can buy the game on a variety of platforms.
Sonic Generations http://en.wikipedia.org/wiki/Sonic_Generations
Oh my goodness, so much nostalgia felt in this game and the music is perfect, totally worth it if you can run the game on high settings. On Steam.
A sandbox like game where you can build basically everything and anything. Updated often and there is a free mode available too. Bought from minecraft.net.
Portal/Portal 2 http://en.wikipedia.org/wiki/Portal_%28video_game%29
A puzzle game from Valve which is awesome. Portal 2 adds a Co-Op element which is fun to play with friends. Available on Steam and Xbox 360 and PS3.
Commander Keen Series http://en.wikipedia.org/wiki/Commander_Keen
My favourite of the series would be Secret of the Oracle. A fun platformer which you can buy from Steam.
Quake/Quake 2/ Quake 3 Arena http://en.wikipedia.org/wiki/Quake_%28video_game%29
As a kid I loved playing shooters and Quake was one of them. You can buy the game(s) from Steam.
Pokemon Series http://en.wikipedia.org/wiki/Pok%C3%A9mon
Probably the only RPG I like to play. I don't have any set game I like the most either so they are all equal.
Doom Series (1, 2 & 3) http://en.wikipedia.org/wiki/Doom_%28video_game%29
Do I really need to leave an explanation of this one .
Some people say it's a 2D version of Minecraft but both games are very different. So much exploring to do and it's fun to play with friends. Available on Steam.
This game is just so much fun. Is has an arcade vibe to it and having extra friends over makes it an even better experience. Available on Steam.
The Binding of Isaac http://en.wikipedia.org/wiki/The_Bin...8video_game%29
This game style reminds me of Zelda a lot yet with really dark elements and is really really hard but I love it so much. 5 bucks on Steam, totally worth it.
Serious Sam Series http://en.wikipedia.org/wiki/Serious_Sam
This game is a fun FPS and has humorous lines like Duke Nukem 3D. Serious Sam 3 is even more awesome and you guys really should have this game in your library. Available on Steam in their HD versions.
And that's my list. I'm pretty sure everyone would know at least one game on this list.
Feel free to post your Favourite Video Games.