Yell.com is my main channel for getting new business.
I do very well with them and have been happy with the product. Although they are not pleasant to deal with and use an overly aggresive sales technique. I just told them to back off or I'd be off and they toned it down.
I have a 'heavyweight' yell.com ad, which came in a package along with a Yellow Pages quarter column ad, and a 118 247 entry (useless).
Here's my heavyweight ad, it usually comes up either 1st (sometimes 2nd) under 'carpet cleaning' for Durham and Sunderland.
http://www.yell.com/ucs/UcsSearchAction.do?keywords=&companyName=carpetzest&location=&scrambleSeed=60334564&searchType=advance&M=&bandedclarifyResults=&ssm=1..........as you can see, it's not much to look at!

but the link to the website gets me a lot of traffic.
Cheers,
David.