Apple refreshed its notebook lineup during WWDC in June. Tim Cook has mentioned that Mac Pro refresh will only come in 2013. iMac and Mac mini are the two remaining Macs that are without any refresh even with the abundance of next-gen Ivy Bridge processors.
The time is almost ripe to finally see some spec bump for iMac and Mac mini. Slashgear has reported dwindling 27-inch iMac stocks in big name retailers including Best-Buy and J&R. We predict that Apple will refresh its remaining Mac lineup with the launch of OS X Mountain Lion. Apple can only confirm that OS X Mountain Lion will launch in July with no specific date.
Beside processor bump to the latest Ivy Bridge Core i7 and USB 3, the new iMac is likely to sport NVIDIA GPU, a transition from the AMD graphic processor used in past iMac. The question remains if there will be new Retina Display model for the new iMac.
As for the Mac mini, the upgrade is expected to be minor with the inclusion of Ivy Bridge processor and USB 3 ports.