I always like to rewatch these shows:
Sherlock: I love the team of Benedict Cumberbatch and Martin Freeman. They play off each other so well, and Mark Gatiss makes a very good Mycroft.
Twin peaks: Kyle Maclachlan is amazing as Dale Cooper, and the fact that it had David Lynch not only as the writer and creator, but also had him star as Dales' superior, Gordon Cole, made it an instant favourite in my book.
Doctor Who (The Jon Pertwee era, specifically the ones that have UNIT play a big role in the story. I love Brigadier Lethbridge Stewart)
Law & Order: Criminal intent (The Goren and Eames episodes only. Vincent D'Onofrio is the reason I started watching it, and he didn't disappoint)
Friends: Its a bit of fluff, and gives me a heady rush of nostalgia. I especially love Chandler and Phoebe.
Blackadder. My dad and I often watch it together, along with classic Doctor Who. Blackadder goes forth is one of the finest written and acted comedies out there, and the finale always sends a shiver down my spine.
The very early seasons of South Park: I am talking about seasons 1-5 here,I managed to stumble across it on a Friday night when I was 10 years old and my dad let me stay up, and I loved it. I enjoy the later seasons as well, but seasons 1-5 will always take a special place in my heart.
There are many others as well, such as Black books, Frasier, QI, Grim adventures of Billy and Mandy, Courage the cowardly dog, Mythbusters and Penn and Tellers: Bullshit!, but the ones I described are the ones I rewatch the most.