If you're going to use it for running (as your sig indicates you did with the MZ), I'd stay away from the hard-disk based portables for now--they're just not built for the shock.
I just got through shopping for a flash player, and found that the one for my needs was the MPIO FL100. My main requirements were: shirt pocket size, SD card expandability, and good sound quality, for around US$100. That narrowed my choices to the RCA Lyra 1071, Rio Cali/Chiba, TDK Mojo, and Digitalway MPIO FL100 (all 128MB models). Since I wasn't able to find the TDK locally, it got tossed out of my candidate list immediately, but it may turn out to be a decent player, so if you find it, give it a try and let me know.
The remaining candidates:
RCA Lyra
The good: Small; relatively large display; shows up as a USB mass storage device
The bad: There was a very annoying constant electronic whine (internal EMI issues?), even when paused; very "barebones": no backlight, no extended menu, no radio...; somewhat awkward design
Bottom line: It'd be worth it if they sold this for $40-50 as an SD drive with MP3 playing capability. Circuit City's no-hassle return policy was made for trying out products like this.
Rio Cali/Chiba
(I tried Cali, but they're basically the same player)
The good: Decent sound quality; good menu system; FM tuner; seemed like most durable of the bunch; stopwatch functions
The bad: SD slot is hard to get to
The mediocre: I'm not a big fan of the "RioStick" control, but tastes may vary; while the display wasn't any smaller than the others, it seemed like it was (may be an effect of the recessed setting and amount of data on-screen); not really made for a shirt pocket
NOTE: I tried it in-store with a pre-written SD card full of songs, so I don't actually know about the software.
Bottom line: Good, but didn't fit my tastes. The Cali may be your best option for a player to use while running.
MPIO FL100
The good: Good sound quality; decent menu system; fairly well designed controls; stylish but unobtrusive; firmware seems to be updated frequently; can recover from (and resume in the same spot on the track) SD card ejection during play
The bad: Poor FM reception; flimsy SD and battery doors and hold switch; transfer software doesn't integrate with Windows Explorer (may or may not be an issue for you); Digitalway has taken down their on-site web boards, with no word on when they'll be back up
The mediocre: Plastic-covered mirror face looks nice, but seems like it'll get scratched too easily (I have an iPaq [thus the desire for SD extensibility] and use adhesive screen covers to protect the LCD, so I just cut one down to size, but it's not the prettiest solution); basic play options (shuffle/repeat/folder modes) are made somewhat difficult to change quickly by the complex menu system; easy to hit Next/Prev switch when reaching in pocket for volume control
Bottom Line: The price ($89 at Amazon after $20 rebate, which, unfortunately, is not available in Canada), size, and sound quality (cleaner than either my Audigy or iMP-350; with EX71s, I can tell that the noise floor is there if I turn the volume down to 0 and pause/un-pause, but it's low enough that it disappears after vol 1--with HD497s, it's inaudible) made it the best choice for me. It may not be good for running, though--the controls are decent, but it doesn't seem to be designed to be held in the hand for long periods of time. Digitalway is supposedly working on firmware that'll let it be used as a USB mass storage device, but don't base a purchase on that.
My advice: Don't listen to me.
Find players that meet your own spec requirement and buy based on those findings. If you're not looking for expandability, the options are much wider, but when you can buy a 256MB SD card for $60, it seems worth it to me to go with something you can upgrade. The MB/$ ratio for a flash player is going to be awful either way, when compared to even the MicroDrive based players, but you don't have to worry about etching the platters if you drop it or just shake it the wrong way while jogging.
Good luck.