I originally found the idea of new races exciting as well, but I soon came to realise it wouldn't be such a good idea. It would be better for Bethesda to focus on and refine the races we already have, and new races means that they need even more voice acting for each line in the game, which means less space, which in turn means less interesting dialogue. I wouldn't mind seeing a different race, but as a playable character? No.
Looking at Oblivion, they should fix the ones they have before they start adding any more. I want my gravel-voiced Dunmer back! The VA was in Fallout 3, so I can only hope he'll be in TESV.
I like the races they already have.
Dunmer
Altmer
Bosmer
Orc (Orsimer, to some)
Redguard
Breton
Nord
Imperial
Khajiit
Argonian
They need to be more distinct, both visually and in abilities, attribute bonuses, and skill bonuses.
Depending on the location (Province) of the next game, I'd like to see at least two of the sub-species of Khajiit.
Or, at least more choices for physical variety (not just faces) - skin/fur/scale tone, height (tall, average, short), and body type (bulky, normal, slender).
GFT
The ten races we have are good enough, the lore behind them is rich and they have a potential to be very diverse and interresting. Beth should try to make the NPCs and even the PC to reflect the lore better, add more variety and overall concentrate on existing races.