For unbiased comparisons, try...
www.avweb.com
...if you find it amongst all the noise, graphics and other chaos, there's a section called 'articles' on the bottom left. Click on 'reviews', and you'll find quite a few good GPS reviews.
I bought a Magellan 315A about 9 months ago. Cheap, cheerful and a good introduction, methinks, before stumping up more on one of the flasher units.