Play.com have the Nexxus Drivespeech Pro Bluetooth Car Kit for just £24.99. This is cheaper than I've seen it elsewhere (such as Amazon). Delivery is free to the UK.
If your order is over £50, remember that you can get £5 off your order by using the code "CREST081". If you wish, you can purchase via QuidCo.com which would give you £1 in cashback (4%).
The text to speech announces the caller name or number, and supports multiple languages (caller's name announcement only works for specific phones - for others it can only announce the number).
Simple user interface, clips onto car's sun-visor. Also supports voice-dialling, if your phone supports this feature.