G4 is running yet another one of their "Best Of" competitions, this particular one is called "Videogame Deathmatch: The Greatest Story Ever Told." Half-Life 2 is currently up against Mass Effect, with over two days of voting left.
To see the entire list of games and to show your support for Half-Life 2 and Valve, you can see the brackets here. To go directly to the HL2 vs. Mass Effect page, go here. Be sure to continually check their site, and to keep voting for Half-Life 2!
Portal 2 is also in the running up against Final Fantasy 7, be sure to cast your vote there as well!