Oh gosh when I'm not watching some new programme I'm constantly rewatching other shows!
The main two I rewatch are Lost (probably seen >10 times) and Grey's Anatomy (seen 5-10 times dependent on the season)
Recently finished a GoT S1-3 rewatch with my friend who was watching for the first time. I'm currently in S2 on my Grey's rewatch.
I've also rewatched the entirety of Scrubs a few times, Doctor Who, Desperate Housewives too.
Oh, and I marathon viewed Parks&Rec over the summer, all 5 seasons in about 2 weeks
I tend to buy TV DVDs of shows I love and then rewatch them. My collection takes up multiple shelves and is very substantial. I shudder to think how much it all costs together.
... I may have a problem