Monique's stories ranged from fluff to angst, and everything in between. She brought Willow and Giles together effortlessly time and time again. She also often made them jump through hoops before they could be together. A few of my all time favorites are: At Last - a true romance; the Defenders Inc series; and Viva Las Vegas. Go read all of her stories at her website Between the Dream and the Reality
Another fantastic W/G author is Laura Smith. Where to begin with the praise? Graduation Present Series is an epic fic exploring the ups and downs of Willow & Giles' relationship. Her A La Carte series made me see the yumminess of Ethan when he sometimes joined in the fun, along with Buffy. Of her one-shots, I'd have to recommend Private Instruction, Phantom Waltz, and Forbidden Fruit - and that's just the tip of the iceberg. Her BtVS fic can be found here.