Building/playing a Pure Caster mage now, first mage origin I'm taking all the way through, most ended up getting deleted shortly after Lothering due to lack of continued interest. Current in level 14, completed Orzammar and the Tower. Had some issues initially with spell choices that ended up with several character falls and a few wipes (Mostly at facing the broodmother at level 9-10) until I respeced and really focused more.
Current spell list (since respec made when taken largely irrelevant)
Winter's Grasp - one of the bread and butter attacks/CC spells
Frost Weapons mostly a stepping stone to CoC, but useful when you know you're facing a lot of cold-vuln enemies like Rage Demons)
Cone of Cold - Good damage but mostly Crowd Control, though melee companions often get caught as well, ah well.
Blizzard - Good damage/CC and half of Storm of the Century.
Lightning - Another B&B damage for few/scattered targets when AoE are impractical.
Shock - Damage cone and stepping stone.
Tempest - See Blizzard, but with more damage and less CC.
Drain Mana/Mana Clense - Stepping stones.
Spell Might - SotC requirement and always nice to boost the odds of the CC effect landing.
Mana Clash - Enemy-Mage-go-bye spell. Mages, Abominations, Demons... Anything that uses magic can be nearly one-shotted with this.
Mind Blast - nice for when the game doesn't let me decide on how/when to engage or close quarters.
Force Field - Good CC to take out problematic mobs or just ease fights. Mostly a stepping stone.
Telekinetic Weapons - Constantly running, better AP for melee is rarely unappreciated.
Crushing Prison - Force Field + damage, great for anything Mana clash doesn't kill. Or if it's on cooldown.
Blood Magic - some fights last long enough to drain mana, lets me keep using spells.
Group Heal/Revival - Secondary healing and resurrecting, not a priority for this build but it's proven useful.
Drain Life - Stepping stone spell.
Planning Blood Sacrifice and Wound next spell choices, finishing out Drain life to Curse or Mortality and Death Cloud and at least the first two hexes and glyphs.
Gear wise, things are limited until I get GP really built up (end game, in other words) until then I got
Senior Enchanter's Robe,
Libertarian's Cowl,
Final Reason (though might trade out for
Shapereat's Belssing),
Sash of Forbidden Secrets,
Key to the City,
Pearl of the Anointed,
Frostshear and
Spirit Hands.