I use iCabMobile for web browsing, the options it gives you is great.
For PDFs and cbr/cbz files, Cloudreaders has been the best I've used so far.
And until the official Facebook app hits the store, Friendly is great.
I tried to get through an issue of the digital comics preview, and it was like smashing myself in the face with a hammer. Sucks that's the only way to get Nick Fury.