My opinions are:
Bretons: Give them a light, lyrical voice and a faint accent. I liked the voice in MW for female Bretons, but I don't know whom to suggest for the males.
Imperials: The Oblivion voice for male Imperials was fine, in my opinion - proud and alert without being too overbearing. I liked Morrowind's too though. LET'S SEE WHAT YOU'RE MADE OF!
Nords: Oh my god, this is where we need the biggest improvement. The males need to have a strong, badass accent like Morrowind's did, as opposed to sounding like Fred Flinstone with laryngitis. Can the extroverted Wonder Woman female voice altogether, and get something more like the voice actresses used in Beowulf.
Redguards: Always loved the voice actors for the Redguards. Michael Mack in particular has been doing them ever since Cyrus from, well, Redguard. Definitely keep.
Altmer: For the Altmer, I think the inflection of voice matters far more than the actual sound. The ones in Morrowind always had this vain, smarmy way of speaking that absolutely has to return.
Bosmer: Ugh, they all svck. I think that the male elf voice in Oblivion would fit quite nicely with some of them, however.
Dunmer: I'm a bit torn here. I do want a nice raspy voice for the males again, but after seeing how awkward it was in the Oblivion E3 demo I'm not sure how well it would work out. Jiub sounded pretty good, but personally I would be content with voices that are simply low and brooding. Regardless of the lore explanation, I've always felt the male Dunmer to possess a lot of machismo, and they would try to make their voice sound imposing just for the hell of it. For females, just use Morrowind's again. So hot.
Orcs: Like the Altmer, the Orcs' means of speaking should be the most prominent contrast amongst their voice actors. Do you remember the crude, slow, barbaric way they spoke in Morrowind? Something like that. No flowy well-spoken Orcs, please.
Don't know what to say about the beast races. I just hope they actually sound as if English (or rather, Tamrielic lolol) isn't their first language. They should have some very thick dialects.