As Dee mentioned already, that board is compatible with socket 1156 Core i3, i5, or i7 8xx CPUs.
The Core i7 CPUs are quad cores with Hyper-Threading. This means you get 8 threads of processing power. These chips have 8MB of cache. These would best suit your needs if you plan on doing a lot of video work, or any application that you would benefit from more than 4 cores.
If you don’t need more than 4 threads but want a quad-core CPU, go for an i5-7xx CPU:
The i5-6xx chips are new dual-core CPUs with hyper-threading that are based on Intels new 32nm process. So they will have much lower power consumption. They also have built in GPUs. Not quite sure how this works if your Asus motherboard needs a discrete videocard anyway. Maybe someone else can chime in regarding this.
The Core i3 CPUs are also dual-cores with hyper-threading. They also have the integrated GPU which you probably can’t utilize with that mobo.
This might explain all this better than I have: