Well I tried to search but did not find anything real on a SDRAM controller... And adding a FPGA is perhaps not the easiest way to go...
Maybe if Craig would try to answer a couple of questions, the requirements would go lower and alternative solutions might be found:
- do you really need so big memory? Do you will ever need MORE than this (expandability)?
- has this be fast for reading, fast for writing?
- nonvolatility?
- is processor execution power precious (e.g. can you afford 50% processing power for SDRAM management/refresh)?
- are there many spare pins on the mcu?
- if a programmable logic is to be used, would it have also an another function, or just as a SDRAM controller?
- how would a FPGA be configured - from the mcu or from a standalone configuration memory?
- what about power consumption/thermal budget?
- is price an issue? (I know the answer for this: of course it is! :-)
- is it board space/device volume critical?
- how fast after power-up should this be ready to run?

Jan Waclawek