Addition to Maria's recs - the
eFiction Book Club? They don't only review ebooks, and they've only reviewed a few so far, but this sort of thing is a step in the right direction, I think.
One other recommendation I'd make - learn to critique reviews on ebook listings. Look at the reviews for a book you're interested in, and judge if they're a) sincere and b) from the sort of person who'd enjoy the same type of books you would.
Many ebooks seem to have bogus reviews on them these days, both negative and positive - but if you read carefully, you can generally work out if they've been written carefully and thoughtfully, or tossed off in a fit of passion (no double-entendre intended).
One thing I'd like to see on Smashwords is a 'most reviews' sort mechanism - very generally speaking, the ebooks with more reviews will tend to be worth at least considering.