The i5s are probably the best bang for the buck now. Just decide on your absolute max budget and then buy the strongest i5 you can find at that price.
The stronger CPU you can buy now, the longer you can go before you need to upgrade the CPU again.
If you can afford say $230 for a CPU, you may be better off buying a $150 CPU and an $80 solid state drive. An SSD can often add more overall satisfaction than a somewhat stronger processor--and the SSD will likely last for several upgrade cycles without needing a replacement.
It all depends on your primary purposes for the PC. If the stuff you do isn't particularly dependent on CPU horsepower, an SSD may be a good idea. But I'd try to stay with an i5 unless you have unusual requirements or a very small budget.