Well, if you're getting Sky TV anyway, I'd recommend Sky Broadband.
It'll be far cheaper than any of the others.
I've had it since Feb. No problems at all, other than ones caused by my own extension wiring (since sorted).
Whoever you go with, plug your modem/router into the master socket if possible, or at least make sure your extensions aren't crap.
Also well worth getting a filtered faceplate:
http://www.adslnation.com/products/xte2005.php
May find this helpful -
http://www.cableforum.co.uk/board/63...-and-info.html