A week ago I bought a new “toy”, a Sony E-Book Reader, and so far I am extremely satisfied with it. I’m using Calibre to manage my virtual library: the Sony Reader preferred format is EPUB and Calibre deals with it very well.
Calibre has also several nice tools to tinker with it: a plugin API (it’s written in Python!) and some command line utilities. By using the latter I’ve built two rusty scripts: the first can be used to download a Wikipedia voice, make an EPUB of it, and put it into Calibre; the second does the same stuff but with generic web pages: it’s less optimized than Wikipedia’s tool (for example you will not have a reliable Table of Contents in most cases) but it does a decent job.