See
E-book Reader Matrix for the details of the Nook and Kobo touch options and the not yet released Sony PRS-T1. The latter is lighter and can directly download from your lending library via WiFi, but it has not yet been seriously reviewed.
As Pomtroll mentioned, the Sony PRS-350 is a smaller basic reader (no touch screen, but very good quality hardware) and you can get a good price now if you can find it in a local store.