ezPDF does, too.. it is able to directly take files from Dropbox, Google Docs and from a direct web connection!!
It also reads epub, naturally (I'm saying that 'cause the name seems to suggest a simple PDF reader)..
EDIT:
actually my biggest problem is that I'm not able to use my Nexus directly with Calibre on Linux..
I tried to plug it on Win7 and Calibre recognizes it as usually; Using Slackware Linux Calibre works normally with my smartphone, for example.. but not with Nexus 7.. I suppose it is related to mtp file system used by Nexus.. but.. I don't know what to do..
reading this thread now I'm setting up things like that: I connect a folder as virtual Android device with Calibre; then I'll put a simlink to this folder into Dropbox folder; then from Nexus 7 I'll connect to dropbox someway (ezPDF opr dropsync or other) and download epub files..
a little bit long but actually I think it's the only solution..!!