Besides the biggies - Kindle, Nook, Kobo, Google eBooks - I've also heard good things about Aldiko and FBReader. Check out Wattpad too - some really great stories are on that site, and they have a great android app as well (although solely for the stories you are following through the site).
Actually, this article has some decent info: You are not allowed to view links.
You are not allowed to view links.
For anyone with apple products (feel free to totally disregard otherwise):
I'm a die-hard Stanza Fan (not android - iPhone, iPod, iPad, mac and Windows only). Bookmarking, highlighting, ability to group books into user made categories...and best of all ability to download shared books from public OPDS catalogs or over your local network (w/ software like Calibre). So I can wirelessly download books straight from my calibre library into Stanza for immediate reading. I can also download books straight from the Wattpad OPDS catalog, and any other site that catalogs their books through OPDS - plus add a webpage for an bookstore if I am interested in direct purchases. It also saves your metadata so you can reread the book synopsis, etc. They updated Stanza so its compatible now with ios5 for the iPhone. However, since Amazon has purchased it, I'm almost positive no more updates are in the works....abandoning such an amazing piece of software is awful! Especially since I have never come across another ereader app that comes even close to this one - and its FREE! I tried a few paid apps solely for the ability to download books through OPDS, but they have no bookmarking or categorizing capabilities. (Okay, I'll stop with this rant now)
Also - I LOVE Instapaper and Read it Later - both great apps. You can install web browser bookmarklets that allow you to simply click a button and save a page for offline reading at a later time. I use it a lot with blogs I follow. Both have android apps (although I'm not sure if the Instapaper android app is from the actual developer, but it does sync your articles across devices well enough). Easy to read and easy to forward saved articles onto other apps such as Twitter, Facebook, Evernote, etc.
One last note: this is only for iPhone (book cataloging apps) - but I use Book Crawler and can't say enough positive things about it. The developer is totally amazing and helpful too.
Sorry the long-winded response! Hope some of it helps.