...Oh, jeeze. I watch way more television than I would like to admit. Hmmm.. Have you checked out Orphan Black? It's in it's third season right now and is Sci-Fi.
Supernatural is always a favorite of mine but it's a long watch, just finished it's 10th season.. That being said seasons 1-5 are by far the best. It's Horror/Supernatural.
The Strain only has one season out but it was fantastic. The second premiers in July so it's a great time to catch up! Finally something bringing Horror back to Vampires. Another Horror genre.
Oh! Oh! Fringe!! I can not recommend this show enough, it is just incredible. It follows a team that investigates Fringe Science events. Sci-Fi with a bit of Horror.
For something lighter Arrested Development is fantastic! It's super, super funny. Humor.
There is a hilarious UK comedy that I am in love with called Black Books that's worth a watch.. 3 super short seasons. It's about a completely anti-social owner of a book store.
If you haven't seen it yet Freaks and Geeks is a must watch! Judd Apatow created and you get to see the starts of Seth Rogan, James Franco and Jason Segel. It only ran for a season but it has a huge cult following.
More good Horror: Hannibal. You wont believe this thing airs primetime on a major network.. Fair warning, it is hella dark but the performances and cinematography are just so beautiful. Only 2 seasons with another starting next month.
And finally, another mainstream favorite, The Office (US).. I just find it one of the funniest things to watch and I rewatch it at least once (probably more) a year. It's a time investment with 9 seasons in total but so worth it.
I could give many, many more but I would drone on. :P