Games with lots of DLC for collecting?

Hitman

Crusader Kings 2 and pack game + all dlc's is in promo now -75% :D

Pinball Fx2 has many tables. They've been twice on Humble Bundle and are also affordable now and then on sales. I like this pinball and can recommend it, as long as you don't need tables which could be realized 1:1 in reality.

Hitman Absolution

Payday 2

Almost all steam CoDs...

dungeon defenders? not sure if they switched over to a goty style pack though

The ultimate answear is Rocksmith

The only game I can think of off-hand, that hasn't been mentioned yet, is Euro Truck Simulator 2...there isn't as many DLC as everything else mentioned but there's a decent whack of them

Rocksmith 2014. Literally at least 3 DLCs per week.

i have the frontline tactics complete dlc pack as a gift

pretty good for DLC and dot hunters:
PAC-MAN™ Championship Edition DX+

Street Fighter X Tekken 61 DLC
http://store.steampowered.com/app/209120/

all paradox games have a lots DLC

The only game I don't see mentioned, yet, is Talisman. I don't foresee them running out of new DLC's for the next ten years.

Saints Rows 3/4, tomb raider, borderlands, street fighter, any EA game and sure how can i forget: DLC QUEST