I don't know about any that are "good for mages", but UB, SP, Mech, and Ramp are all pretty easy on the heroic level. I would think any instance that needs cc is going to be very mage friendly. I would try to get into any heroic groups you can and see how they go. Most heroics fail b/c of under-geared tanks or healers in my experience, very few times has it been b/c of sub par dps.
There is also a nice wand off the last boss in UB too if you try that one out.
If you don't have a focus macro, now would be the time to make one for polymorph, it will make your life much easier in heroics/raids.