There's going to be a big performance difference between your original Vertex and any new drive, on paper. In reality, you're not going to "feel" a difference. However, upgrading is a good idea if your Vertex is malfunctioning (not surprising) or you just plain need more space.
Pursuant to that, the Intel 530 that Essence pointed out is a good deal at in the 240 GB range. It is however, a Sandforce drive with all the usual Sandforce peculiarities (history of bugs, unrecoverable performance loss when filled, very different performance for compressible vs. incompressible data).
So if you'd rather not get one (and I don't blame you), the
240GB Crucial M500 is $155 and the
480GB version is $300. Surprisingly, the 500GB model is actually better cost per gig (barely).