If you want the best and are willing to spend above $300+ then it's either the Core i7-2600k or i7-2700k.http://www.anandtech.com/bench/Product/203?vs=287
If you want to spend less, then you should be able to find an AMD Phenom II X6 1100T for around $200.http://www.anandtech.com/bench/Product/203?vs=288
The Core i5-2500k (~$215) comes very close to the Phenom II X6 1100T, however since it does not have Hyper Threading it does not do as well as the Core i7-2600k for Photoshop batches and video encoding. The extra 2 cores in the X6 1100T helps.
I know that the Core i5-2500k is easily overclockable to 4.5GHz, but I'm not sure how high a Phenom II X6 1100T can be OC'ed. Therefore, the i5-2500k may be better than the X6 1100T if you are willing to OC.