Actually, I just completed a build using a Phenom II X4 955 which was on sale for $99 from Tiger Direct and it's awesome! I combined it with the Gigabyte 880GM-UD2H mobo and, for now at least, the integrated 4250 video is fine for MCE. I'm probably going to add a discreet video card at some point due to some slight lag navigating menus while playing h.264 live TV (HD-PVR fed content) but as far as a price/performance comparison on the mobo/CPU front, I don't know if it's possible to beat that combination. And the performance is just great! I run DTb and ShowAnalyzer on the same box, with 2 HD-PVRs hanging off of it, and it never misses a beat, even when analyzing 2 shows, recording 2 shows, and watching a bluray .mkv rip all at the same time. And all of that is happening only using the integrated 4250 video, which is the weak point of the build. Not too shabby when you consider that the mobo/CPU only cost me $178, which does not include the $15 mail in rebate for the mobo.
This build replaced a Zacate build that I did about 3 months ago. What a nightmare that was. The Zacate is great for watching video only! MCE screens were sluggish at best, all other processes needed to be offloaded and it still choked regularly on me. I do not recommend the Zacate solution to anyone interested in any kind of performance.
The overall project replaced a 4 year old Athlon 64 4600 MCE build which has finally been retired to my office, and I'm actually typing this post on it.