There aren't a whole lot of options using a full atx motherboard. The case has to have room for it so I'm not sure if these dimensions are what you'd consider 'htpc' or not.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811163257
I'm not sure if this one has to use the included psu or not.
http://www.newegg.com/Product/Product.aspx?Item=N82E16811144231&cm_re=apevia_x_master-_-11-144-231-_-Product
http://www.newegg.com/Product/Product.aspx?item=N82E16811119265
Just be sure to read the specs of each case, make sure your existing psu will fit. Make sure whatever cooler you plan to use for the cpu will fit, many have limited options for air coolers (above various heights, usually needing low profile air coolers) or limited mounting choices for aio water coolers if supported at all.
Generally speaking in terms of htpc's your components aren't ideal. An fx 8350 isn't an overly efficient cpu which means fairly high heat output which can be a problem keeping it cool in a cramped htpc case. Something like an i3 or i5 with much lower tdp (heat output) would be more ideal. Also your motherboard is a full atx unless there's another model of that board I'm unaware of. That means your htpc case can only be so small and still be large enough to support that motherboard. Many htpc cases tend to be micro or mini atx for that reason.