(a) I am prototyping a new CPU (Harvard Architecture) 

with separate 1MB  program memory and 1MB  data memory. 

Which Xilinx FPGA board would be the best choice for separate external memories?

(b) As another option, is a 2MB external dual ported memory possible on any

FPGA board? 

Hi rsdivekar

Would you be using the FPGA only for the architecture and no other application thereafter?

I would suggest go for a moderate cost FPGA and purchase an external memory interface for 2 MB

(Thanks for the prompt reply!)

Yes that is correct. Primary use of the FPGA will be to implement the CPU

core. 

can you suggest some off-the-shelf memory interfaces?

A plug in type SRAM architecture may not be available. Try ML561. You could additionally search for "Xilinx evaluation board with SRAM" on google.