The "Yugrin" series of levels for MotS (I think it was MotS) was interesting.
Of course everybody lauds the "Warzone" series for JK as some of the coolest ever, and they have some legitimacy to those claims. ; )
There's plenty out there I haven't played. I just got through downloading a few hundred levels off of Massassi (and their hosted page Admiral's Command Chamber) plus the files from HyperView and JK Academy here on JK.net, so I have a lot of levels to sort through!