I have an ancient TomTom GO 300 which I've had for the best part of 3 years now. I've kept it updated and the maps are about a year old. Still works just as well as it did when I bought it, and the battery lasts about 4 hours on a full charge, so it doesn't have to be plugged in.
I have used the newer TomTom ONEs as well, and found them to be just as good, although I have heard that the new slimmer models don't have as decent battery life. Most people keep them plugged into the car charger anyway though, so it doesn't really matter. I would wholeheartedly recommend TomToms. They're a household name for a reason!
Mine was about £300 when I bought it, and they are amazingly cheap now by comparison. The more expensive ones offer you a lot more for your money, although if I were to update I'd probably get one of the lower spec ones since my needs are pretty basic. Hopefully other ABers will be able to give you more specific advice.