There are Prime-based algos (Rie, Prime, Gap), Blockchain-based scratchpad algos (Wild Keccak) and memory-intensive ones (Cryptonight). Can take a look at
http://cpucoinlist.com/. These are all based on high random access memory requirements which GPUs perform poorly with.
These are mostly well-established algos with known optimised GPU miners, actually. But the main difference is the GPU miners don't have much of a Hash/Watt advantage over CPUs even after heavy and public optimisation, whereas for Dcrypt it could be a lot higher and still private.
Alternatively, we can also focus on PoB for the masses, and just use an established Scrypt or SHA256 PoW for miners.
Now I'm not much of a miner, but my only worry about an asic friendly algorithm would be that especially early on after the switch it'd be easy for one person to get all the blocks. On the flip side, cpu-only means someone with a botnet can do the same thing. Tricky decisions.