VirginMedia are doing a Mobile Broadband offering for existing Cable and ADSL customers from £5/month (1Gb usage):
http://allyours.virginmedia.com/html...nd/mobile.html
I've just signed up for this, having spent my lunch hour trapsing around the local shopping centre playing the operators off against each other. The dongle is free (although there's a £4.88 shipping charge), the contract is for 12 months and costs £5/month (for my usage level) and my dongle would have been delivered tomorrow, but I asked for a Friday delivery.
To get the £5 offer you need to either be a Cable L or XL subscriber, or be on Virgin Nationwide Unlimited. The offer expires at the end of June. Other T&Cs apply. The only painful bit was being passed from VirginMedia Customer Services in Newcastle to Virgin Mobile Customer Services in Liverpool to Virgin Mobile Sales in India!!!!!