if you look at the dev (or was it tech) forum, you'll find my eprom cart design there. not as nice and fast as a flash cart, but it works. also, it might be possible to actually use flashroms instead of the eproms, so at least the deleting wouldn't be needed anymore.
Standard 32-pin Flash should work in those designs if pin 31 is bent up (it should really be pulled to +5V, but can probably be left unconnected) and pin 1 is connected (and lifted if necessary) to its pad instead. For a related reason, I'm pretty sure that there are no 8Mb flash devices in 32-pin DIP packages, so it might be necessary to use 4Mb devices and change the address decoder's connection accordingly.
edit: didn't see this part the first time around:
Are you starting it out from scratch or basing it off other flash carts?
I've not seen another flash cart design to really base it on, but the design was inspired by certain elements of Mike G's SMSReader (which is designed for writing to SRAM, but isn't fundamentally limited to SRAM).