Unfortunately, just like the music, Blizzard doesn't actually credit the talent part by part, so while it's easy to find a list of who's voiced something in game (the IMDB entry is probably the most comprehensive, as it contains all the names from the booklets to both shipping WoW and Burning Crusade), finding out who's done what is a little harder. Tony Jay did the intros for all the races, and Cam Clarke has been pegged as the male Blood Elf (among others, including Nexus-Prince Shaffar and Medivh). Voice actress Erin Fitzgerald has done quite a few voices in Burning Crusade, including Dorothy and the Wicked Witch, as well as Sarannis and the Essence of Desire in the Black Temple. Kath Soucie, another well known voice actress, has also done voices in BC, as has Michael Dorn (yes, Worf).
But most surprising on the list is probably the sheer number of Blizzard employees-- some, like Samwise Didier, Chris Metzen and Mike Morhaime, are well known, but others, like Tracy Bush, Derek Duke, and Glen Stafford, are usually working on the music of Azeroth. And even others-- Michele Arko, and I'm sure a few other names that I just don't recognize, work in completely different departments of Blizzard, from QA to Administration. So it seems like they invite a lot of their local employees to come in and record voices for their games, and not until recently, with the Burning Crusade, have they turned more often to more high profile actors.
Unfortunately, that doesn't exactly answer the question of who the female Night Elf is. But especially for the shipping game, odds are that it's someone who works at Blizzard, not a professional voice actor.
Update: You guys are the best. A reader of ours is friends with the Night Elf voice, so here she is: Debi Mae West. And yes, her goods really are of the highest quality. Apparently, she was also Meryl in Metal Gear Solid.