I had a couple of Navmans. Admittedly, they both broke, but I found in terms of function they were better than any other I've used.
Made the mistake of buying a Binatone. It was very cheap but, unfortunately, absolute shite. I gave up using it entirely because it was so troublesome.
Garmins are good and reliable.
For a good deal, check the Tesco /Argos / Currys outlets on eBay. They sell stuff cheap and it's generally perfectly good catalogue returns.