Now that I think about it, FM2 might be pretty overkill for an HTPC. A 100 watt CPU might be a bit much for small form factor solutions, especially if noise is an issue (more heat more fan ramping). You could go with the lower wattage Athlon:
http://uk.pcpartpicker.com/part/amd-cpu-ad740xokhjbox
except the price is almost the same, so you might as well go with the faster solution.
Intel is a really good option. Any Ivy bridge or Haswell i3 would be more than enough for an HTPC and it would run cooler too. Some higher end i3's have hyper threading so you get 2 cores and 4 threads if that is something you're after. If you want to go mega budget friendly, you could go with an Ivy/Haswell Pentium or Celeron too. I see some people use them for HTPC's.
http://uk.pcpartpicker.com/part/intel-cpu-bx80646g1830
http://uk.pcpartpicker.com/part/intel-cpu-bx80646g3430
Quad Core solutions: This Xeon processor on the Ivy bridge lineup is an interesting option (Albeit overkill, but if you want a low wattage quad core CPU):
http://uk.pcpartpicker.com/part/intel-cpu-bx80637e31220v2
This doesn't have onboard graphics, just like the Athlon. It's a bit more pricey than the lowest end i5 on the Ivy Bridge line up, however the Xeon is a lower wattage CPU that runs cooler. You could go with Haswell options as well, they have the respective parts, they do draw a bit more power though.
Now I know most motherboards are compatible with the Xeon's on the 1150/1155 socket's, but I don't feel like being responsible for anything, so do your research before hand.
If you NEED a quad core (which you don't for an HTPC), I would just go with something on the FM2 platform.
I would personally go with an i3 Haswell solution on the 1150 socket, and a pentium if you want to save some cash. Second choice would be something on the FM2/FM2+ platform.