You could take the Arcane Warrior spec and just use Shimmering Shield - a very good shielding spell. I often play a pure caster mage with Spirit Healer as first spec and AW as second and don't use Spellweaver or armor, but stick to spells. Shimemring Shield can help you out, if you are surrounded by melees. But of course, saving the second spec for Awakening is possible too. I really like Keeper and Battlemage - no one will ever harm you again in melee
(ok maybe some of the bosses, but the rest - not so much)
My new favorite spells are the Mana line. Especially Mana Clash - nearly always a one hit death for Darkspawn emissarys or other enemy spellcasters - and it works on shades too. Great spell. I just mention that, because I seldom used that spell tree before and was often frustrated with the amount of damage, emissarys did to my group, especially in the deep Roads.