The TomTom iPhone navigation software has been available on iTunes since last month. Now the TomTom Car Kit for the iPhone 3GS is listed on the UK Apple Store for £99.95. The car kit appears on the homepage, but currently the link to the product page does not work.

The TomTom Car Kit has an external GPS receiver integrated that is supposed to be better than the one found in iPhone 3GS.
The TomTom Car Kit is supposed to include software.