Would be very helpful if you could list your components,particularly the motherboard, is it ATX or M -ATX etc. Is your graphics card one of the larger/longer ones. This will have a bearing on case size. Are you looking for silent or one with lots of places to put LED fans for a bit of bling? Do you want your case windowed? What is your budget.
I have just built a HTPC which required a small silent case, my last desktop is water cooled so needing a larger case.