Thats for sure, picked mine up for $20 and I can't even remember how long ago I bought it, over a year at least.
Portal is also available as an arcade game on the 360, so you have a few choices. The Orange Box is more than worth it though, as Nimrod and Dark Scyth say its a great package.
My top 5 1. Fifa World Cup 2010 2. COD MW 3. Gears of War 4. Red Dead Redemption 5. Need for Speed Shift
1. The Orange Box (team fortress 2) 2. Mass Effect 3. Blue Dragon 4. F.E.A.R 5.Condemned 2: Bloodshot
1. Gears of War 1 2. Mass Effect 2 3. Bad Company 2 4. COD: Black Ops (gameplay looks great) 5. Super Street Fighter 4
1. CoD Mw2 2.Halo Reach 3.Condemned 2 4.Condemned 1 5.Gta 4 - Full Edition(Gta EFLC + Gta IV) Top 5 Xbox 360 Games
It's been awhile so i'll update my list. 1. Dark Souls 2. Battlefield Bad Co. 2 3. Duke Nukem Forever 4. Catherine 5. (If it makes a U.S./World release) Monster Hunter Frontier Online
1. Dragon Ball: Raging Blast 2. Sonic: Unleashed 3. Race Driver: Grid 4. Red Dead Redemption 5. CoD: Modern Warfare I'm more of an anime guy and classics, so I'll go with these ones. Really excited for Sonic Generations!