I had a tiny creative Zen V plus sometime back, and it was pretty neat. I couldn't get it to work with my Linux box then (probably because I was pretty much a noob those days), but I don't think you should have any problems the way Amarok is these days. Regarding your other questions:
* resumable playback: No, but maybe the new Zen does this.
* Hold Button: Yes.
* video podcast playback: Yes.
* Playlist management: Dunno, mine's always set to shuffle.
* Tactile controls: Yes, the menus are fairly easy, separate buttons for volume control, etc..
* Around or under $250 U.S: Yes, I guess.
* on board file management: Yes, IIRC.
* track rating system: No.
* Photo display: Yes.
* Audio Book playback: Dunno.
* Simple movie conversion/playback for watching DVDs, home movies, you tube stuff, etc: My V Plus required a specific software I think, to do the video coversion.
I haven't tried Archos and the rest, these days I'm just using my PSP for music (its okay with music but is great as an all-round PMP, even without homebrew).
P.S. Just remember all this is for the V Plus, the new one seems to have quiet a few new good stuff. I'd personally recommend it over an iPod.
P.P.S. The joystick on my Creative broke pretty soon
Its a good thing the new model removed it completely.