Well, an accelerator is always a good area to start. The CSA mega midget racer worked flawlessly for me, and the company is still going! Links below.
Upgrade the Roms, ebay, softhut, craigslist (look in San Francisco area, a guy is selling 2000/500 chips)
There are HD's that go on the side car, that you can also find on EBAY too.
That's the beginning. Look at the A500's that people have posted on Amiga.Org and get some ideas there.
Happy hunting.
