http://www.tomtom.com/en_gb/products/tomtom-outlet-store/
If you're going for the Smartphone route, you can get an Orange San Francisco for 80 quid and CoPilot UK for about £25.
Dedicated devices have the edge in terms of reliability, performance and such. I can't remember my old TomTom ever locking up for no reason or having a duck fit because the phone rang. Why buy a compact camera or an mp3 player?
Personally, if I were getting a satnav tomorrow, I'd get CoPilot for my phone. However, if I was suddenly made a field service engineer (say), I'd want a dedicated device (and a Traffic subscription). Horses for courses.