Breton is a good choice (Resist Magic 25% + 50% absorb once per day). Altmer isn't bad either (50 magicka - equivalent of 5 levels - and super-magicka-regen once per day can be sometimes lifesaving). I would avoid Dark Elves - which some people suggest for various mage-like builds, but they only make sense if you actually want to be in the middle of the fight (whereas my build assumes you avoid the dirty job ;]).