I really miss Angel...much as I liked Buffy, Angel was just the better show, and god damn that ending was AWFUL. But Angel did a lot more with its characters in a much shorter space of time - I mean, it made freakin' CORDELIA likeable - and it was a little more...grounded, maybe? I mean, it was still ridiculously out there - even moreso than Buffy at times - but Buffy's seasons felt very self-contained, whilst Angel told a more cohesive and satisfying story...which ended on the worst cliffhanger ever. Unless you read the comics, anyway. Which I haven't yet. I may do at some point though.
Stargate Atlantis, too. I felt that SG-1 ran its course after season 8 - which made seasons 9 and 10 extremely painful to sit through - but Atlantis...Atlantis was just getting started. They could have easily gone for a sixth season, and I really wish they had, because as much as I hated the Earth-based episodes of SG-1, with Atlantis actually on earth at the end of season 5 it could have been verrrrry interesting to see what they did with it. Plus I wanted more Rodney. You can never have too much Rodney McKay.
Also generally I miss the days when cartoons were actually good, i.e. the 90s. I've seen modern day superhero shows and they don't hold a candle to X-Men, Spiderman, or Batman: The Animated Series. Imagining what the team behind the Marvel shows in particular could do with some of the better modern day comic book storylines is an exciting prospect. I find myself missing Batman: The Brave and the Bold sometimes too though, if only because it was more light-hearted and it actually nailed it pretty well at times...it also gave us the Music Meister, the greatest character in DC's history, ever. We need more characters like the Music Meister.