Hehe, there's a simple mod that lets you use the Portal gun in HL2...it's pretty sweet, but it doesn't work on all surfaces, just mostly flat surfaces. It definitely offered some funny fights though.
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )