Thanks, Gstaff! :goodjob:
Fliggerty - for his amazing scripting contributions
The LGNPC team - for making Morrowind NPCs less boring
Korana - for Solstheim Castle, Pelanor, the Provincial Bath Shoppe and a ton of other mods that brighten Morrowind
Princess_Stomper - she's been blogged once already, but she's recently released The Holiday Mod, Balmora Council Club, and is working on Dance of the Three-Legged Guar
Emma - for her and Grumpy's contributions to companion scripting
Timeslip - MGE
I would recommend more, but there are a lot of modders who've made huge differences but have unfortunately left the community.
Excellent list there. Definately Cyran0 and Ostar of the LGNPC team are worth a look. (Or whoever the actual boss is, I'm not entirely sure)
I might also recommend some of the admins from the big mods like Silgrad Tower (not sure if they still work for Morrowind, or who their admins are) and Tamriel Rebuilt (Haplobartow, Lady Nerevar, Thrignar Fraxix).
Not sure if he's still part of the scene really, but GhanBuriGhan is still around these forums, mostly in the Fallout boards, and he was the creator of the excellent Morrowind Scripting for Dummies guide, as well as the Travelling Merchants mod. I don't think he's an active modder any more, though.