The DLC for Ninja Gaiden 2 is amazing if you have that. A lot of the standard missions it comes with kinda suck, but the weapon survival missions are basically the best thing in any action game ever.
The All Fronts pack for Gears 2 is a pretty good deal if you still care about Gears.
Minerva's Den for BioShock 2 is supposed to be pretty good, but I've never played it.
There's a bunch of alternate costumes you can buy for (S)SF4. Those are pretty cool.
The Fallout 3 DLC is pretty decent for the most part, but you can just rent the GotY disc, install the DLC, and send it back.
You're probably better off buying some XBLA games. There's a ton of great ones like Trials HD, Bionic Commando, Mega Man, Geometry Wars, OutRun 2, Afterburner, Ikaruga, etc.
Also, I agree about all these GotY/Platinum editions coming with all of that overpriced DLC for free. From now on, I'll just be waiting for the complete version of any game that's sure to get a bunch of DLC, with some rare exceptions.
So far I've got the new Alan Wake DLC, the GoW2 All Fronts pack, and I'm probably going to buy Super Meat Boy this Wednesday. Not sure what else to get. I'll probably just buy the Valkenhayn DLC for BlazBlue CS.