Do you live in a cabled area? I've been with NTL for about 2 years and have been very happy with the service. They are doing an offer of free installation and free modem for a 600k connection at £24.99 a month (see here.) They do cap the service at 1gb a day.
ntl: home's broadband and dial-up services are intended for normal recreational or educational use by individuals and families and our pricing and network architecture have been designed accordingly. Customers who use the services more heavily than a normal home user will reduce the performance of the network for other customers.
"Normal use" of the service is defined as up to 1 gigabyte downstream of data transfer daily (which equates to approximately 200 music tracks, 650 short videos, 10,000 pictures or around 100 large software programmes downloaded per day).