Enchanters, in non-undead heavy campaigns, are actually pretty good at low levels. Just carry some other options with your non-specialty slots.
Evokers are good with Dazing Spell, but they don't really blossom until level 9.
Earth Elementalists get a lot of the core conjurations in their specialty slot options and are very good before level 5 (when they are grounded due to fly being in their opposition school, which isn't necessarily a huge deal.)
I really like the foresight diviners school powers, but like the evoker, it really comes to its own as the bonuses become greater.
Color spray is another early fight ender, which would keep the illusionist's specialty slot for level 1 filled, and level 2 has some of the best illusion spells in the game.