Get the X4 620. It's a great budget CPU. I wouldn't mess with any of the Intel CPUs under $150 because most of them suck. AMD controls that part of the price bracket. More cores is always better. Future apps will be using multitheading.
+1 to X4 620
It is a good chip and can be built on an AM3 motherboard. With an AM3 motherboard you should be able to upgrade the pc in a few years instead of doing a full rebuild. Just be sure to get quality components.
Well, when the 6-cores come out from both AMD and Intel, I'm hoping for a price drop. But things have been going up recently despite new hardware coming out. nVidia's cards have sky rocketed in price for some reason and all DDR3 ram has gone up too. I have seen some prices come down so that might be a sign of good things to come.