Online Travel Booking and Bidding Agencies - Websites Where You Can Book a Long Layover?

I'm planning a trip where I want to have a long layover in a city on the way home (6+ hours, but still same day). I'm pretty sure I've seen a website where you can go about requesting a long layover but have searched the forums and can't seem to find it. Can someone point me in the right direction? Thanks.

Any of the airline websites will allow you to indicate when you want to travel.... so getting a long layover will be no problem.

However, Priceline and Hotwire will not allow you to specify long layovers.

I'm actually looking for a very specific website that I found through these forums a week or two ago, I just can't remember the name of it. I remember on the display after you searched for a flight they were listed in the bottom half of the screen and it said "long layover" or "short layover", I believe in different color fonts. I just can't remember the website. Any help is appreciated, thanks.

www.kayak.com

opodo always gives loads of possible combinations, including some long (even overnight!) layovers...