Well Droid 3 is ideal-ish as it's an OMAP 4 (so the Pandaboard stuff should be reasonably close), however as it's a Motorola phone, it's probably not so easy. In addition it's not available in the UK and as GrimyHR says it's expensive for a device that will be unusable for most of the time (i.e. while developing for it)

Desire Z is a Snapdragon, so you'll end up with the issues as listed on the Meego page.

The Hummingbird is somewhere between the two, no drivers directly available, but potential to modify and use the OMAP4 userspace stuff.

Life would be much better if all the SOC manufacturers released GPU acceleration libraries for both hard- and soft-float....

In any case I'm continuing development on the Hummingbird, noting that one can now buy a 1GHz, 512MB RAM Hummingbird machine (w/ GPS, e-compass, WLAN, BT, etc.) in the form of the Samsung Galaxy S Wifi 5.0/4.0 for ~£130.

If you want something that has compatible drivers + userspace for the GPU, then a Tegra 2 device is the way forward, but they are mainly 10" devices, which is not what I'm after.