I've got the Navman F20.
I did a little looking around and found a decent price on it, so went for that. I don't use it all the time, so didn't see the point spending too much money. It has a memory card slot so you can load the maps for Europe, etc if you take it abroad.
It also has the option to show you points of interest on the map like hotels, cash points, stations and by default it will always show petrol stations and car parks, it even has two special buttons which when pressed will give you a route to the nearest Petrol station or car park.
Also it will give you a count down and warning for speed cameras (the fixed ones) and will warn you if you go over 72mph, but it doesn't tell you what the speed limit of the road is.
All that said, it's pretty good for £120ish.