Using an Arduino to act as the external interface to the 6502, giving you full control of it. Via Hacker News
The 6502ctl project is an Arduino controller for the 6502 CPU. The controller controls all 6502 pins, including the clock signal and interrupts, and simulates an address and data bus with attached memory and an output peripheral. The controller includes a clock-cycle debugger with disassembler. An assembler is also included with the project.