I've always wanted to make my own Atari cartridge, and this project is a perfect excuse to give it a shot.  I have some old Atari development cartridges I bought on eBay, which unfortunately accept only old eproms that dont match the pinouts of modern easily available flash roms.  There were some schematics online for some updated carts, but they didn't make use of the bank-swapping available on the 130xe.  So here's my take on it:

It's basically an update of a design Atari used back in the day for their later games.  It has 256k available and can be programmed without removing the chip (using a special programmer I have in mind).  You could go as high as 1 meg, but I wanted to stick with through hole components.