My i-mate jamin (aka: o2 xda neo, qtek s200, htc prophet, dopod 818pro) is the closest i have found to a perfect device.
With a 4gb sd card its a pretty good mp3 player (around 15 hours playback, wired phones, volume at 100%, 200+kbs bitrate). Would be really cool if mc(12) could sync to wmp mobile db and read playcount from device... (Or a MC mobile that could be used as a standalone mediaplayer on the road(as mobile networks becomes faster even playback from home computer) and be a remote over wifi to control htpc or simmilar when at home?)
I used it alot with a bluetooth gps this summer when driving around in spain, "saved my life" when trying to get around in the narrow streets of seville
Things that could be better:
1. A wifi chip that did not suck the battery dry.
2. 3g
3. Built in gps.
4. A bit smaller so it vould fit better in my pockets.
5. Updated bluetooth with native a2dp
6. Faster cpu an more ram.
7. better battery.
(I used to think my iPod was the coolest think ever until it broke and I called Apple "support".
There is actually a pretty good song about Apple "support" by The Rakes called Itrouble)