I just got done with the Wool series. It's 5 quick books but they recently rolled it into 1.
http://www.amazon.com/Wool-Omnibus-H...tt_at_ep_dpt_2
The first two books were a little slow (character development and what not) and the last 3 were constant action with a couple of great twists.
I've been reading a ton of post apocalyptic books recently and this as one of the better series IMO.