I have had 3 TomTom's and much prefer them to the cheaper varieties - Garmin, Navman etc.
However, I have in the past bought TomTom's with the built in bluetooth, but they are not that good so would recommend against getting a one with integrated bluetooth or MP3 player.
There are 2 map sources, but you'd be surprised the difference the s/w makes. TomTom is by far the most accurate, ask anyone who uses GPS for a living. TomTom is still basic & lacking in features and lags behind the competition in most other respects, but makes up for it having an extremely small footprint. Voice instructions on TT are far superior to anything else too.
Personally I wouldn't touch Garmin. I use iGO8 that does 3D landscape plus buildings; traffic alerts & speedcams on a cheap chinese clone.
Beware maps covering large areas. They are significantly shorter on detail than country specific ones.
Just a vote for those on a tighter budget, the Navigo units from Ebuyer (Navigo GPS Sat Nav - UK Map, 4.3" Widescreen, Full Postcode Search ALSO plays MP3 & MP4 - Ebuyer) are fantastic! Running Windows in the background and very hackable - the software comes on the flash card, so all you need to do if you want to run a different navigation system is buy an extra flash card, install and off you go.. Huge community for modding them etc and they're also MP3/MP4/avi players if you want a small screen for watching something on when you've got wherever you're going and got bored... :D
You might want to consider the choice of mapping data as part of any evaluation. There are two base map data service providers, TeleAtlas and Navteq. I have used satnav systems based upon both and generally find the Navteq data to be more reliable & accurate. If I where in the market for a new PND I would be looking at Garmin products. At the moment I use a TeleAtlas based Via Michelin X-980T in my car. However I have still not forgiven it for giving me audio instructions to turn left while giving visual instructions to turn right while navigating through Haarlem... not funny when you end up in narrow streets in a 7.5m motorhome!
I have just started playing with a Navteq based Garmin Mobile PC running on an MSI Wind in my motorhome, the 10" screen takes some beating.... but it's a bit big for a normal car dashboard :)
A good website to get more information about GPS & satnav in general is Pocket GPS World - SatNavs | GPS | Speed Cameras
Bought a portable Tomtom One XL in June with FM Traffic Updates... its been preety good. Other car has got a built in radio/cd/nav system in the dash.. and its OK... its neat to use and alot less hassle, but alot of the manfacture OEM units dont take postcodes for some reason... :censored:
@broc: you have to pick the mapping data for the country tho'. The strong choice in one can be the weak choice in another.
@TechMonkey: The features added to newer versions of TomTom are copied from the competition. There's just too much to list. Configurable spoken warnings including speedcams. iGO is configurable with customised skins so you can have practically anything you want. There's even a high res TomTom skin.
Great skin here: screenshots
Just to add that TomTom has bought TeleAtlas if not mentioned already...