O2 Broadband. If your an O2 mobile customer they knock a few quid off their monthly rate. My old man just switched and it costs him Â£10 per month with free wireless router which is a faultless bit of kit. Free tech support over the phone and everything came through the post quickly. I think it's a limitless download on a 16mb connection, although he gets 14mb (the maximum the line supports).
I set up my laptop inside 5 mins with it's wireless connection. I was impressed with it. He's had zero problems in the two months he's been using it.