Right now I'm using the Spartan 3A FPGA starter kit from Xilinx. All the other "hardware" is actually synthesized inside the FPGA: a 68000 soft-CPU (TG68 core from opencores.org), 32K RAM, and 8K ROM. The synthetic RAM/ROM sizes are much too small, but are all that would fit inside the FPGA. They're enough to create a screen buffer and run the initial boot code from ROM, anyway.

I have an Altera DE1 board on the way, which has real external SRAM and Flash ROM that I can use. (The Spartan 3A board has DDR RAM that I could never figure out, and ROM that can only be programmed through a serial port.) I haven't yet decided whether to add a real 68000 to the DE1 on an expansion card, but given how easy it was to get the TG68 soft-CPU working, I'll probably stick with that.

Eventually I'll need to construct an expansion card containing a microcontroller and some other things, but I should be able to get pretty far with just the Altera DE1 board. The DE1 is an "educational" board with all kinds of miscellaneous gizmos. My long-term goal is to make an all-custom Plus Too board that contains only the parts actually needed.