Sky Broadband: Free, for a bit
They say: "We’re so confident in our broadband that we’re offering existing Sky TV customers the ability to switch to Sky Broadband Unlimited on a 3 month free trial. If you're not happy within 3 months you can leave without paying a thing."
If you're not a Sky TV customer, you can go whistle.
This 'no commitment', 'no set-up cost' and 'no line rental cost' is helped by the fact that, if you already have Sky TV, half the hard work is already done and they don't have to send a man 'round your house to fix it up for you.
After the trial, if you like Sky's service, it'll cost you £7.50 per month and a Sky line rental will cost you £16.40 per month. There's cheaper deals out there, that's for sure.
If that sounds like your thing, visit Sky's offer page.