UMPCPortal is the place to see all "bigger than Nokia 770" options. Almost all of them are more expensive, and these are all UMPC-like, i.e. not just ebook readers. The Raon Everun (4.8" screen) is interesting, with a long battery life and is "only" $700 (in the US). Another possibility is the One Laptop Per Child XO-1 see
G1G1 v2 to start on November 17 and cost $399.