24 (2001-2010)
Just finished this series. I have to say I quite enjoyed it and am sad to see that it's over. But I am glad my favorite character made it through to the end! (Not Jack)
Star Trek: The Next Generation (1987-1994)
I was caught off guard that I had finished these two series so close to each other. I was expecting to finish 24 with the X-Files. Anyway, it was a great series. It's a shame they didn't use all of their feature films to tie up various loose ends from the series like First Contact did. I think that's also a part of why Wrath of Kahn was so good.