www.scan.co.uk
www.overclockers.co.uk

Ebuyers are fine till you have to return somthing. then they leave a little to be disired.

Microdirect are good to deal with too.

Consult
http://users.hexus.net/companies_list.php
For user submited reports on any company you may wish to try out in future. Could save you a lot of hassle :)