The Abhorsen series is available from fictionwise.com, among other e-book sites, in Secure Mobipocket, Microsoft Reader, Adobe Reader 7, or Palm Reader formats.
Baen Books is the best single source for sci-fi e-books for any e-reader (no DRM), but it still mostly includes Baen authors - although others are coming round. The first of a series is often in the
Baen Free Library.