Tough call...
I think the price for the X4 955 is pretty low. However, I don't really track CPU prices. I don't think it will drop any lower until Ivy Bridge comes outs; March 2012 to the best of my knowledge. However, I don't think the price will drop much more. Probably down to $110, unless someone is having a sale. It might hit $100, but not for a while; longer than you would to wait.
Again, I don't really track CPU prices. If and when I feel the performance of my current PC is no longer good enough for me, then I'll upgrade without being too picky about prices unless there is a confirmed announcement that CPU prices will be cut relatively soon.