After devoting a majority of the weekend to beta3, I've enjoyed:
Mage Slayer/Fighter: Good damage, support, and some defense through Rapid Recovery. Since he can't use potions or scrolls I fill his inventory with explosives and noise makers to set up ambushes. Modeled after Torian Kel from Arcanum.
Darcozzi Paladin/Priest of Wael: Popular build on these forums for all the right reasons. Spectacular tanking abilities with some extra support on the side.
Rogue/Skald: Great at breaking armor and setting up afflictions for sneak attacks.
Beckoner/Evoker (or /Priest of Berath, Lifegiver): Summon a hoarde of skeleton minions before the enemy's midline to body block and mess up pathing. Then blast away with Fireball (summoning more skeletons!), cast Berath afflictions, support allies, etc. Hilarious with the Flames of Devotion upgrade that copies the effect on to nearby allies - would the Bleak Walker FoD add its bonus effect?
Priest of Eothas/Lifegiver: Solid support all around, though I find the shifting mechanic clunky and Rejuvenation spells have less than perfect range and AoE. Investing in Arcana adds even more versatility.
Beguiler/Ghost Heart (Wolf Spirit): How I saw my main character in Pillars 1, and what I'll go with when the game launches. I especially enjoy Charming enemies from stealth, and the wolf spirit can soak a good bit of damage. If Cipher cast/recovery times get reduced, I might go with Beguiler/Sharpshooter instead, but this is my Watcher's best thematic option.
Assassin/Sharpshooter: Fun for a while, but it's gimmicky, selfish, and falls apart quickly. Might be okish if Invisibility effects beyond the costly Guile skills are reasonable to come by.