To start with, I think we are going to need to narrow down generally what people are going to need to sound like for each race, then apply the geography and other factors as we narrow things down to the specific character or group of characters. Now keep in mind, this is an open discussion, My opinion of what a race should sound like is just that, an opinion, feel free to express yours, you may have a better idea than I do.
Humans: Humans are the shortest lived race in the game and therefore the most versatile vocally speaking as they tend to develop their own quirks depending on region and who they live around. While they will not always pick up the accent of the other races, humans in general tend to pick up (and distort) each others accents, thus giving us the widest variety of accents to work with. As humans are going to be very much environmental and regional, I suggest we table them until we narrow it down to particular geographical areas in the game.
Dwarves: Being a race of miners has developed a very gruff language structure. Most assume a Scottish style accent when thinking of a dwarf, and although not a bad idea, because of the variety of dwarves in the game, I dont think it should be the only idea. the environmental factors for dwarves are going to be the constant rock dust, hard exertion of mining or other feats of strength, and being a long lived and hearty race with a quick and surly temper.
Gnomes Although gnomes do live underground, even in their own city of Gnomergon, they were not the ones that did the digging by hand, and therefore do not have a dusty feel to their voice. As a race they are known for being overly curious, usually to a fault. Highly intelligent, inventive and energetic has led to their voices usually sounding like they just pounded Red Bulls and helium. Although the excitement has usually been captured in the voice, I feel that there needs to be a bit more passion for the engineering that shows through, somehow. Perhaps a bit nasally.
Night Elves: Elves in general are a much longer lived race than any of the others in game. Night elves in particular are a very spiritual race, and as they are long lived, usually very wise. In game their speech patterns have been characterized as slow, almost the point of sounding stoned on something. I think it might be time for a change in the way that they sound. Perhaps if we can find a balance between the wiseness of the American Indian and the accent of something slightly italian? Post if you have different and/or better ideas.
Draenei: These are a unique race, once a proud people, now having to be humbled from fleeing the outlands, their voices tend to sound a bit over the top. They are firm believers in the Holy Light, and as they tend to see the world in black and white and take a very "Paladin"-like approach to things, most Draenei aare charactarized as being part of the Dudley Do-right club. Personally, I think a major revamping of the voice needs to happen for them. I think if a russian accent was applied, it would be more fitting. the Russians always having been a proud people, trying to make it through harsh times and harsh climes, they still reflect strength and confidence in their voice.
Well, that should get us started, I will start a post about the Horde shortly.