I've been very tempted to try one of those TomToms.
I used a Garvis (I think) when renting a car, and it had some serious lack of features, such as typing store names and such. It also got angry with me when I wouldn't follow it's driving directions exactly.
I'd highly recommend Garmin over TomTom. I have a Nuvi 670 but also used a TomTom (can't remember which) when I was vacationing in Florida for a week. The Garmin's directions have been more clear and accurate. I can't recommend a device that will tell you to "keep right....turn left" on a busy 2 lane street, such as with the TomTom.
I have a Magellan Maestro... 4050, I believe. It's a pretty decent system, and it's getting a map update soon. It also runs on a Windows CE core which means that it's fun to hack it to shreds. Mine can now run Explorer and has a few games, a calculator, viewers for Microsoft Office formats, and an all-in-one media player similar to VLC.
I have experience using Navigon, Garmin Nuvi (Not street pilots...wanna get one though), and Magellan Maestro. Out of the 3, Nuvi is the most user-friendly and easiest to modify your destination on the fly. Navigon comes in last between the three and is a bit slow. Magellan is a good happy medium and can do a little more than Nuvi, but I found it a little more in-depth to use.
All 3 have models under 150 and are top notch for US and UK for their pricepoint. I use the Nuvi 250 (basically the 200 with wide screen