Soon the easier question to answer will be which major tech company doesn't have an e-reader model. Asus has thrown their hat into the ring with the DR-570 e-book reader, and it's battery life is staggering.
But what is key here: the Asus e-book reader is said to be able to run 122 hours on a single battery charge. And that's not standby-mode (supposedly).
No word on prices yet, but it should be available before the end of 2010. Who knows what e-reader pricing might be like then, but with a color screen and battery life that long, it won't come cheap.