Silian Wizard Edit
I find myself to be a fan of the Silian Wizard because the feral ult packs enough of a punch when I need it. During the first few levels I place all my skill points into hp to make sure I have at near 900 hp so I do not have to worry about healing as constantly.
Afterwards, I switch gears into int and wis in (3:1) ratio for the benefit that comes from healing. I do not worry about having dex at all because I have no reason to run in battles. The wizard's attack stuns almost every time and I have no need to worry about running out of mana because the wizard automatically recharges mana under 50%.
After int hits 80-90, I switch gears again to worry about survivability in Act 3. Overall it is a fairly balanced build.
Monkeyball (Freeze + Barrier Wizard) Edit
Something I'm still tweaking, but really liking the results of so far. Wizards are usually pretty squishy. However, you can get insane MP regen and get bonus ATK with barrier up, in addition to the nice DR. So, this guide centers on keeping your barrier up for fun and profit and surviving big hits to the face.
Play safely and cautiously until you get barrier. Even after getting it, you probably want to be overleveled a bit and stack up plenty VIT prior to the Reaper...that fight can be really tough due to his damage output.
+2 VIT and +2 INT at each level up, and take the HP-increasing passive each time. You might also want a few points in the armor passive - but I haven't done the math to determine if this is "worth it" yet.
Magic mastery is a must for the MP regen it gives - we'll need it to keep a multi-stacked barrier up. Equip heavy armor and shields wherever you can for bonus mitigation.
For class advancement, I chose Frostborn. 5% chance to freeze enemy on attack and 5% chance to freeze enemy when barrier is up. You also regen even more MP and rage points when the enemy is frozen.
For race, I went with Human but Kraste might have been a better choice. Kraste means even more freeze chance, plus higher damage potential. I chose Human for the rage boost; being able to hunker down for a few turns then unleash a feral ult is awesome, especially when it also restores all your MP.
Gameplay is basically "keep least 2 barrier stacks up while whaling away on enemy until they fall down dead". Heal as necessary...you'll need lots of heals early on, but when you can support a few barrier stacks this build really starts to shine. Run away from manathreshers since they will make you cry.