If you're talking performance parts, then there could be almost anything that will make your car gain low end torque.

Otherwise, you might want to consider a tune-up and some maintenance issues. For instance, an intake service would help. This would clear out alot of clogging that may happen in your intake manifold, as well as some of the cylinders. An intake service also requires additives being added to your fuel when you fill up. This cleans out the fuel injectors. Actually, I highly recommend this service because in my GS-R, once I did it, I noticed a MUCH better throttle response, and my car felt a little quicker.

Other maintenance issues may be electrical, such as spark plugs, spark plug wires, distributor rotor and cap. Maintenance is required so your engine doesn't fail in a certain department. So, you know, just some things...