CS:S hasn't really changed in the last few years. I play the odd round of Gungame which is a pretty fun mod. Definitely get Orange Box for Portal and TF2. Portal is really fun, loved it, and TF2 is the only multiplayer game (besides Left 4 Dead) that I play, it's a really really fun pub game, a lot more fun than CS:S in that regard.
I'm not sure which product I've gotten more value from, Orange Box or purchasing original Half-Life 1 CD in 1998 and getting literally thousands of hours of gameplay from HL1, HLDM, CS and DOD (mostly CS, I'm actually glad they didn't track total player time because from June 99 to around Christmas 2003 I must have logged 3000-5000 hours in that damn game). With Orange Box I've put about 500 hours in TF2 since Nov 2007 plus EP2 and Portal. Point being, you get so much value for these products it makes my laugh when people were ranting about the pricing schemes when Orange Box was released.