I would suggest you to not so rush and take your time and wait for recommendation for the motherboard.
One thing for sure is that if you are building a new build, avoid Phenom II at all cost! This is because a i3 2100 deliver the same performance as a Phenom II X4 at 3.8GHz in even games that uses all 4 cores such as BFBC2, and in games that are not design to use all 4 cores, the Phenom II X4 will fall behind the i3 2100. Also not to mention that a Phenom II X4 at 3.8GHz under load is rougly double the power consumption of the i3 2100 (140W vs 65W), as well as running much hotter and need a beefy CPU cooler, whereas the i3 2100 chilling even on the stock Intel CPU cooler.
If you MUST go AMD, wait for Bulldozer and don't go Phenom II!
And ignore the Fragg's quote for "i7 can be overclocked further, but if you were to overclock you would have to invest in a cpu cooler instead of using the stock cooler which comes with the processor", as we are talking about SandyBridge here, not last gen Intel platform. The i5 2500K can be confirm to be able to overclock and 4.0GHz fine at reasonable temp even on the stock Intel cooler. Also, he doesn't seem to understand Phenom II's limitation, particularly in games that uses 3 cores or less. In CPU demanding games that doesn't use 4 cores such as Total Wars series and WOW, the Phenom II will be streets behind the Intel platform...not just current gen SandyBridge, but last gen i5/i7 as well.
Also Phenom II will bottleneck Crossfire/SLI of two current mid-range/high-end cards, because its aging K10 architecture is simply far too slow in today's standard.
So simply put, if you are getting a new build right now, right this moment...you should go Intel SandyBridge. But if you are not in a hurry, you can wait for AMD's Bulldozer (should be out very soon) and reviews on it, before deciding to go Intel or AMD.