In no particular order:

nemeara  - because he / she always adds something that challenges the poster's point of view, although, more often than not, it is done so subtly that the poster does not, nor does anyone else for that matter, know just how his / her point of view has been challenged.

Moose  -  because, although I haven't heard from him in quite a while, understands the issues better than anyone, it seems.
The Yell - because he's really intelligent and witty.
Einstein - because, although he's clearly a twit in SO many respects, is very, very smart.
Red Fokker - because he's about as disillusioned as I am.
Skoe - because skoe is a mod now, and so it is always good to include at least one mod in such a list
Justinian - because, even though he's clearly a bit off, argues his points well
Han / Godman / ... (who knows what other nicks he / she uses) - because he / she is so typically Chinese and, therefore, so much fun to aggravate. 

There are others, but I don't recall your nicks off-hand, probably because you don't post enough!