Here's a little about the spec I like:

18 Arcane / 43 Frost - http://www.wowhead.com/?talent=o0xE00cZZbAMIsfxsbsz

Key talents on the arcane side are Clearcasting, Magic Absorption, and Arcane Meditation. Magic Absorption is dominating when you are in a place like SM:Cathedral-- you will resist all the casters will you and it's an endless stream of mana, allowing you to keep spamming Arcane Explosion or Blizzard after Blizzard.

Frost side is a standard AoE Blizzard setup with some points that I wouldn't normally spend in places to help mitigate damage or improve mana efficiency even further. Beefing up a frost bolt is not a priority, since it is almost never used.

My basic setup is to keep Ice Barrier and Mana Shield up at all times, and run around using Rank1 arcane explosion and ice lances to aggro/pull a region. Get all the melee folks into a nice little clump at some point, Frost Nova, and Blizzard them all down while the casters shoot spells at me hopelessly. They keep my mana high, and then I kill them last by LoSing them around a corner and getting them into a big clump to Frost Nova/Arcane Explosion. Shatter is nice on lowbie mobs, since you get a lot of crits this way. If a pull goes horribly wrong, I usually pop an elemental and use its root to re-establish a good Blizzard routine. I never blow cold snap on a frost nova first.

Anyhow, that is what works for my specific situation where I've been grinding the lowbie instances over and over and over and over and pleasemakeitend!