Generally a dual core CPU is good enough to run a HTPC. Pair it with a Radeon 6570 and you got a nice HTPC setup. So AMD Athlon/phenomII x2 or x3's do fine, same with Intel i3's.
Depending on if you have cable or not: Ceton InfiniTV 4
$299.99 is expensive yeah, but comes with 4 tuners. So you can record 3 while watching one. And it can be shared over network to other machines in your network as well.