I just got a cheap bluetooth one to use with my phone - with a dodgy copy of TomTom is worked brilliantly... until I broke the power/usb port
Back to my old Nokia and printing off directions from Google maps now!
www.ebuyer.com have got some good deals and there's thousands on ebay, but I'm thinking of getting another Windows Mobile phone or pda to use with the GPS I've already got as I'm kinda used to TomTom.