i think it is worth also to consider a sort of hdd-gpu-cpu mining rig hybrid. which should be the best option in future.
GPU mining as usual - probably ethereum or something more profitable. (genesis mining is my favorite if you can pull it off)
CPU mining works best with Monero or Electrum soon. small money for the cpu mining, but why not use it...
HDD mining is an interesting thing. Burstcoin does something like this at the moment but its not very profitable. things will change when Substratum pulls out their p2p-internet attempt, where you will be rewarded for hosting chunks of the internet(data) and there are more coins like this. Siacoin (cloudstorage), MaidSafecoin (p2p internet) and many more.
i'm not saying its worthwhile at the moment, but its definitely something to keep an eye on ;)
cheers and happy mining