I tried a few different ones, but finally settled on a large chinese jobby from DealExtreme.
Linky
Yeah, it's the US version, with outdated maps, but it comes with iGo 8 and the maps are easily obtained. I replaced that with iGo Primo 1.2 and it works really well. I also enjoyed fannying around with various CE applications and addons.
If you find the right files, iGo will accept either Navteq or TeleAtlas maps, supports terrain elevation files (for 3D maps), configurable POIs, replaceable voice files (including Text to Speech for reading out street names).
The only real downside is that the screen is hard to see in bright sunshine, and the battery only really lasts for around 2 hours unless its plugged in. Still, it's only around £50.