I am going to assume that, being an Accord, this is a modified street car aka "daily driver". While I was never much into the Honda scene (except for S2K and NSX), I know a lot of people who autocross stripped down Integras and Civics with K-series or other drivetrain swaps.
I personally think you need to stay away from ANY kind of forced induction including Nitrous until you have a proper suspension, brake, and wheel/tire setup or you are not only wasting money, you are endangering yourself.
That said, I think the following will net you the best gains for bolt ons:
- Ceramic Coated Equal Length Headers
- 200cell Hi-Flow Metallic Cat OR Test Pipe (cat delete)
- Underdrive Pulleys
- Lightweight Flywheel and Clutch Assembly
- Cosworth Intake Manifold (or similar)
- Camshafts
- Lightweight 17x8 up to 18x9 wheels all around (a square setup; D-Force makes 17s that weigh about 16lbs per wheel...), help with acceleration, braking, and handling
I do not know what kind of intake yours is, but it is very much worthwhile to go with a full cold air intake that puts the filter outside of the engine bay and replaces every bit of OEM intake ducting with a 1 or 2 piece unit featuring smooth bends, a heat shield, made from plastic or Carbon Fiber, and wrapped in heat resistant "cloth" or foil. Otherwise, you are losing power.
It does not have to cost a lot either... Since it will be covered, you can use the Spectre Build Your Own intake parts from AAP/AZ/OReilley/Peps/etc. Use silicone gaskets between pieces, minimize length while still getting the filter (afe ProDry cone, ideally) into the bumper. Paint the tubing with High-Heat-Resistant paint after sanding it, then wrap with inexpensive DEI exhaust wrap, followed by a wrapping of aluminum tape to act as a radiant barrier.
Total cost is well under $100 since you already have a cone filter.
In the end, though, you will get much, much more fun out of a car with a properly sorted high quality suspension than a bunch of bolt on engine mods...