I was quite impressed with iPod Nano 4G? (I think that's it). Running 256 AAC was rather decent. iPod Touch 4G is also quite nice sounding unit, and well adapted to using different music player apps, EQ apps etc. one I owned for a while along side other players.
I believe ClieOS likes his 7G Nano a bit.
The closest thing I have atm to an Android based player is the Hum Pervasion, which puts out some striking sound around DX90 levels.
(excuse the quality, I'm not in camera man mode today)
Check its specs out here: http://hum.hk/index.php/products/product-music-player/55-pervasion
I will be sticking with the X3 Mk1 for a while I think. I'm very impressed with this player. So much I ditched my X5. Well, that and what turned out to be a faulty scroll wheel.
3 years R&D went into the X3 and it would not surprise me if because of that margins were low. They may have even lost money on every unit sold. Kind of like the Bugatti Veyron business model - they lose money on every car they sell because of R&D costs. But what a car!!
That's why I think the original X3 will become a classic. I think it'd worth more than what they sold it for.
Anyways, my interests have changed and I've been told I need regular exercise so ultra portable sound for me atm!!