I'm always browsing Kobo's sales. I've found some really amazing books that way (and also a couple clunkers that taught me to always read the sample downloads), plus a lot of books I was already interested in reading. A lot of popular books end up in their sales, you just have to be on the look out for them. A lot of classics can also be gotten super cheap on their website, like a single "book" that's actually comprised of like fifty books for $2.99.