If you are looking for older titles, and can live without the smell and feel of old paper, there are a lot of ebooks available via the Project Gutenberg website.

Gutenberg

These are books for which copyright has expired, so they are free to be shared.

There is a bit of a bias toward American authors (think Zane Gray rather than Edward Grey) and the search function is rather basic, but if you are prepared to dig about a bit there are some great reads.

Most books have multiple formats, so can be read on a computer screen, kindle, or even printed if you want to read in the bath.

Jerry