X-Files, 24 and the Walking Dead for me, at least as far as non animated series' go. Unfortunately, as is often the case, they all went on too long and suffered a drop off in quality as a result, although I'm still enjoying TWD a lot more than many seem to be. The Two Fathers/One Son two parter was the ending of the X-Files in my head canon, the show (especially the Mythology stuff) took a steep drop off after that. At its best though, no other show has gotten me as pumped as that did.