Recommendation for a Book Reader / TabletPC

I've been thinking lately on getting something like the Sony Book Reader. You know with so many information on the net I'm very used to download documents, manuals, even blogs! and read them offline at night. Since I'm not a top computer geek I'm not very familiar with this kind of hardware. I was thinking also that maybe a simple TabletPC or ultramobile pc would do the job, but I'm not sure.

Has to be something realy slim and portable and easy to read with, something you would take with you to bed ( well, not for that you are thing of...).

The idea is that it should be mainly for reading and other features as a bonus. Any suggestion?