There's one very good site I'd recommend enough to write a post about it:
They have a short blurb about each author which includes known pen-names, a section of whatever's expected for release soon, and a main list of titles arranged by series. To the right side is a mosaic of book cover pictures.
Each picture or book title is linked to a separate page (if any) that goes a little more in-depth on that title.
And here's a short list of places to look for e-books:
Universary of Pennsylvania Online Books
Brookings Institute Free Library
Internet Public Library
National Academy of Sciences Free Library
MIT Free Course Library
I don't know much about the others, but Gutenberg has a massive amount of public-domain stuff, like the complete works of Mark Twain and Shakespeare. Everything's in plain-text.
Google recently started offering entire books and magazines available online:
Their interface is okay, but I seem to remember that it irritated me a few months back when I first checked it out. When you're still on dial-up in a high-speed world, it's easy to be irritated.