(In no particular order.)

Ye olde series:
- Elfen Lied
- Berserk
- Aishiteru ze Baby
- Shingetsutan Tsukihime
- FMP

Currently airing:
- Utawarerumono
- Eureka 7
- Zero no Tsukaima

Now, I have to add that I already typed Cowboy Bebop in the list instead of FMP, but changed it after a little pondering. In my opinion Bebop is a better series, but when I think about it in retrospect, FMP probably matters more to me, even if it doesn't reach Bebop's level of quality. But then again I have a series like Aishiteru ze Baby there, so you can probably disregard anything I say...

For the currently airing I placed Zero there instead of School Rumble 2nd season, because in the end despite SR's superior script writing and amazing level of quality I tend to be drawn more to coherent plots rather than individual episodes.