Piecewise said:
Hellsing Ultimate, FLCL (you have to think), GITS...
Screw the episode limit, I love Code Geass
Actually If you consider Geass as 2 seperate series lelouch of the rebellion and r2 then it does fit the episode limit criteria and the one about having a follow up series.
Agree FLCL Is great although the entire show is just fanservice for the maker who pretty much came u with this by just throwing together everything he liked or just liked the sound of.
Excel saga is good but has an extremely annoying main character and has an entire episode devoted to fan service, the no ugly men episode, and has a follow up ova called puni-puni poemy which has some major fanservice but that is mostly for the sake of having a go at fan service.
Full metal panic is pretty good not to much in the way of fanservice lots of action and the romantic subplot is slightly undone by the total obliviousness of the main character has to follow up series called fummoffu and the second raid.
Orphen is a good option.
Want to reccommend cromarty high school there are practically no chicks the only downside for oou criteria is that you could probably define the whole series as filler.
King of bandit jing is ok not much ongoing plot though.
And as a finally the 3 patlabor movies