A warning note: none of the ebook readers have *good* MP3 players; it's an additional feature they threw in, maybe for audiobooks. Read reviews carefully to check how they work; I know that on the Sony device, there's no turning off the mp3 without turning off the whole thing–it has a "pause" function, which still eats battery very quickly.

I have a Sony Reader PRS-505, and I like it very much. (I don't use it for mp3s.) I didn't want a Kindle because I like converting ebooks myself; I don't want to email them to Amazon & have them do the conversion for me. Also, I wanted to use the free ebook sites like http://www.manybooks.net and http://www.feedbooks.com and those are much less useful with a Kindle.

The Foxit eSlick is so new, nobody knows how well it works yet. The discussion thread about it at Mobileread is at http://www.mobileread.com/forums/showthread.php?t=34276

Which reader is best, depends on what kind of ebooks you want to read. The Kindle store has a lot more than the Sony store–but the Sony allows more types of ebooks without the hassle of sending them in to be changed. (Also, I hate DRM and I don't want the manufacturer of my Reader to know every book I read on it. But those may not matter to you.)

The 100 free ebooks from Sony are pretty much worthless–they're all classics in the public domain, available in other places on the web, and the versions for free at Mobileread are better formatted. Don't let that convince you to buy it.

If I were buying today, I'd probably go with the eSlick–but that's partially because I have a full software suite to convert *anything* to PDF, and I can reformat docs so they look nice on the small screen first, if I care to.
References :
http://www.mobileread.com/forums/