Tanga offers the refurbished Dell Optiplex FX160 Intel Atom Ultra Small Form Factor Desktop PC (no monitor) for $69.99 with free shipping. That's $80 off list and the lowest no-rebate price we've seen. (We saw it with a 160GB HDD for $5 less after rebate hassles in October.) Features include an Intel Atom 230 1.6GHz processor, 2GB RAM, 80GB hard drive, and Windows 7 Home Premium 64-bit.
Note: A 90-day warranty applies, although it's unclear who backs it.