I bought the MPIO 256mb FL100 about 2 months ago and I am extremely happy with it.
Pros: Lightweight, small, very expandable (bought a 256mb SD card for it for $100 Cdn), sound quality is good, FM Radio with good reception, just 1 AAA battery with long life (my rechargeable AAA gives about 7-8 hours of playback), good user support from a Yahoo group, leather case has a sturdy clip good enough to jog with
Weaknesses: Bass is a bit weak and there is no true equalizer (just a few equalizer pre-sets), have to use the included software to transfer files but it is simple to use (and includes an auto-firmware upgrade tool which is handy), the leather carrying case needs to be stretched-out first, only USB 1.1 so transfers are a bit slow, included earbuds are not very good, Study Mode didn't seem to work (if you even care about that)
You might also consider the FD100 (?? I think that's the model) which basically has the same features except that the unit is a bit bigger but comes with a wired remote. The remote looks a bit more convenient for clipping to straps.
The FL100 has gotten a lot of very good reviews.