jenshih_blue (Foxhunt2blue) & pet_23 (Pet): I've mostly only read these two gals to write together, although I know they've written with other co-authors and/or alone. The first fic I read by them was Lost & Found, an AU Spangel fic. I was immediately drawn in to the storyline, as well as the characterization. They were big influences in opening my eyes more to the world of slash (although I still will only read a few pairings). Their Spangel - in whatever form they happen to be in - never fails to captivate me, and when the very long chapters come to end, I still wish there was more.
You also must check out Bayou Boys, maybe then Fox will add the rest of the written chapters to her memories (hint hint). Pet's up-to-date, but her LJ is FO.
I also have to recommend Fox's Acrylic Dreams - a very imaginative AU that just keeps getting more interesting.