I currently own a presettlement 30g Zen vision M, My major complaints are that I can't load it from my ancient versions of linux and the battery feels like it's always dead. I think it either has some horrible power leak when it's off, or it's pretending to shut off and not actually doing so. It's about the size of deck of playing cards and the UI is acceptable.
So here are my top contenders:
Sansa view 32g. Price $150-$180. Good stuff: it's slightly physically smaller. It's loadable from linux and is flash, which will make it boot faster. Battery life of 32 hours of music play time. Bad stuff: the UI has no separation for long lists, so if you want to find a specific song to play and it starts with Z, you'll have a long wait and a sore thumb. Since I use it in the car a lot, this isn't so good.
Creative X-fi. Price: $250 This is made by the same company as my Zen. The UI is exactly the same, but they seem to have made the interface standard USB. This is also a flash player. They also made the battery life much better at 30 hours of music. It also has wi-fi, which almost felt worth breaking my budget for, but apparently it's kind of horribly slow. So all in all, it seems like a high price for not much of a win.
cowon d2 16g + 16g SD card, price: $144 + $30 I thought this was the one. It gets great reviews about it's verisitlity, sound quality and touchscreen. It acts like a mass storage device, so the compatablity with loading is huge. It will play ever format under the sun, or so it claims. The SD slot is completly intergrated (unlike the x-fi) so the memory is seamlessly expandable. The sticking point... it chokes on bad ID3 tags. Now I'm sure that I could run a script to clean up all my bad tags, if I could figure out what "bad" is. But I'm kind of tired of high maintence eletronic devices. It's important to me that my mp3 player just work in the car. I can't be having to fiddle with it. The reviews are mixed between those people who think it's be best player EVER and those who struggle with it's inablity to deal with bad ID3. I'm still tempted to buy one, see if MY bad id3s make is sick and return it if not, but I'm not even sure I'm up to that.