The thing is it's a bad time to buy a new pc over the next six months or so as both AMD and Intel are replacing all of their current sockets.
Intel.
Socket 1156 (Core i3/i5 and some i7) is to replaced very soon (next couple of months) by socket 1155. Despite only being a single pin difference, cpu's will not be interchangeable between sockets.
Socket 1366 (core i7) is to be replaced by socket 2011 in Q3 next year.
AMD.
In Q2 next year they lauch the Bulldozer cores which are going to need their own new socket, rumoured to be AM3+.
This is why i suggested a budget build using a Athlon ll X2 and a AM2+ mobo so that you could use your existing ram. Not only is it cheap, it's also a upgrade for you as well.