The more popular American shows get picked up on their stations, often half a season or a season late (as we get theirs). You can especially find them on Channel 4 and its offshoots. Some are current (New Girl, Daily Show, Nashville) and some are reruns (Gilmore Girls, OC, Friends--the latter of which is on for at least two hours a day).
However, there is a channel on their cable called Sky Atlantic that specializes in high-end and well-respected American shows, like Mad Men, Friday Night Lights, The Wire, etc. (A lot of it's the HBO back catalogue.)