I just bought this, the
KOBO ereader yesterday. It's $150, which is a good deal cheaper than the sony or the kindle. It has no backlit screen, which is easier on the battery life, is very lightweight and has a small footprint, which I find great for slipping into my pant's cargo pocket for reading at work. It has a 1 GB internal memory and will take an (up to 4GB) SD memory card. I can sync it to my laptop with a USB cable, download books either from the KOBO site, or from my computer in PDF format, or from my public library in either PDF or EPUB format.
The operating system is licensed under the GNU license, and is free to download to read on your desktop, or on your smartphone. I was reading KOBO ebooks on my blackberry for about a month before buying the ereader tablet. I can sync books between my desktop, the reader and my smartphone with bluetooth, so I'll always be able to pick up where I left off, which can be pretty handy.