People recommending a SSD with the Sandforce controller are right on the money. SSD drives work differently to traditional ones, and the disk itself holds a lot of logic regarding how stuff will be written. Once you have written once to every block on the drive (this does not mean the drive is full, it just will not understand files where deleted on a mac) writing will slow down - sometimes significantly.
Out of the after market drives the Sandforce based models suffer the least from writing on the long term. With some of them you might even end up with half or less the original performance (Intel does suffer less then the worst ones though).
The problem with Sandforce seems to be reliability though. Intel is very good in that regard. The most popular Sandforce drives are the OWC and OCZ Vertex 2.
Sandforce is coming out with a new model this summer which should be blazing fast. Intel is also coming out with a model that should offer up to twice the capacity for the same price, and the Intel should come out any moment now (note, you might have to wait for teh dust to settle before the prices come down to that level). Personally I'm waiting since I'd prefer 300GB of space and the biggest price reductions will probably come to that price point.