I'm interested in mining altcoins, mainly to turn some servers into (literal) space heaters, since it's winter. One thing that really interests me is if an altcoin has been designed to only be mineable by traditional CPUs. The big thing I can think of to cause this is large memory requirements. A large memory requirement for hash processing would cause current GPUs to be slower than CPUs (due to the individual "cores" of the GPU not having enough direct memory). It would also cause ASICs and FPGAs to be very difficult to develop to be faster than CPUs, and expensive. This is because you effectively reduce the mining complexity so that it bottlenecks at the memory bus (which is much harder to significantly speed up)
I'm sure I'm not the only one to have thought of such a scheme. Is there an altcoin out there that is designed with this kind of ideal behind mining?