Warlock/Mage is a very good combo, and Mage/Warlock can be very effective. Many of the Warlock general skills are high-damage, and obviously come from a different "power" pool--Focus, rather than Mana. Not to mention that both classes get to "double dip", so to speak, with a general skill that boosts INT.
I have a Wl/M/Ch toon i've been fiddling with. (Since there isn't an abbreviation convention yet for Warlock, I'm using "Wl".) Reasonably survivable, has two "roots" (Perplexed and Lightning), which gives you a chance to build up Psi points, and the Wl damage skills are almost OP, especially a couple of the elites in the 15/20/25 range.
Wl/P or P/Wl might also be a good combo, but I haven't messed with it or looked at the elite skills for it. Wl/M/P could be the best of all worlds, especially for "cheap" players--all three classes are cloth/staff users, so only one set of gear to manage.
I was just looking at the p/wl elites, because I too was curious.
Psychic Passage
Consumes: NA
When Psychic Arrows hit, this skill restores 50…800* HP to the target's current target. (Upgradeable)
Touch of Revival
Consumes: 30 Focus
Restores 70…1540* HP to all party members in a fan-shaped range of 120. (Upgradeable)
Prayer of Tribulation
Consumes: 30 Focus
Continuously heals a friendly target 4 times. Each time restores 30...660 HP. When target's HP reaches over 40%, the skill increases the target's Physical Defense and Magical Defense by 2% for 10.0 seconds. When the target's HP falls below 40%, this skill can be stacked 2 times at once, up to 8 times. (Upgradeable)
Soul Cleansing Ceremony
Consumes: NA
Cleanse can also remove cursed states.
Spirit Jump
Consumes: 20 Focus
Blessed by the holy spirit, you are able to pull a friendly target close to you.
Spirit Spring
Consumes: NA
Blessed Spring Water can increase the healing you receive.
Holy Salvation Candle
Consumes: NA
Once this is used, your next Holy Aura can be cast on friendly targets. However, the effect time is reduced by 2 seconds.
Spirit Embodiment
Consumes: NA
Summons the Spirit Embodiment. For the duration of its existence, the embodiment will recover 90.0 HP for the party member with the lowest HP every time a spell is cast. It also reduces Received Physical Damage and Received Magical Damage by 10.0% for 5.0 seconds.
Looks quite interesting. I may toy around with this in the near future. Another thing to note is, all of these skills, according to wiki, are instant cast.