1. Twin Peaks (Obviously, or I wouldn't be here) :
I won't bother to justify that one, as we have a whole forum here for discussing TP 
2. Buffy The Vampire Slayer:
I agree with evrything you said 100%. I don't know how many times I've had to put up with people who look down their nose at this show smirking when I bring this up, but I digress. Everything about this show is better than it has any right to be: Writing, acting, directing. It has (along with my #3 choice below) one of the deepest, most compelling and involving mythologies ever presented on TV. And it holds up to many repeat viewings, as I can personally attest.
3. Angel:
More than a Buffy spinoff, it's more like Buffy's darker and meaner older brother. Buffy's signature metaphors of adolesence and young adulthood have their counterpoint in Angel's metaphors of adulthood, maturity, responsibility and parenthood. The mythology gets even deeper here, particularly in the brilliant Season Four. Part of Angel's strength lies in Joss Whedon's underrated collaborator Tim Minear, with whom he co-created...
4. Firefly:
Yep, there's a trend here. I'm an unabashed Joss Whedon fanboy
. Firefly -basically a gritty Western set 500 years in the future with space taking the place of the frontier-is what the "Star Wars" prequels should have been: Dark and edgy, but with a biting sense of humor and slam-bang action. Most of all, it's just plain fun.
5. American Gothic:
This short-lived series from creator Shaun Cassidy (Yes, the one from The Hardy Boys) shares a few things in common with Twin Peaks. Like TP, it revolves around the weird doings in a small rural community. Less stylish and more overtly supernatural than TP, it nevertheless draws you in with a strong mythology, well-drawn characters and one of television's greatest anti-heroes in the person of the town's evil sheriff Lucas Buck (Played with charismatic charm by Gary Cole).
If you're looking for something new to check out, I'd highly recommend American Gothic since you've probably seen all the others on my list. It's on DVD and I think you can check out the episodes for free on fancast.com.
One last thing about my list. With the exception of Buffy The Vampire Slayer, all of these shows fell prey to early cancellation. Even Angel, while it was on for five years, was abruptly axed three-quarters of the way through Season Five. It could have gone on for two more seasons. tells you a lot about how hard it is for quality shows to stay on the air.
By the way, my favorite Trek is Deep Space Nine.
"What? Did your life pass before your eyes? Cuppa tea, cuppa tea, almost got shagged, cuppa tea..."