Newegg offers the refurbished Lenovo ThinkCentre M58P Intel Core 2 Duo 3GHz Desktop PC (no monitor), for $134.99 plus $1.99 for shipping. That's $40 off and the best price we've seen for this configuration. (It's a current low by $3.) It features an Intel Core 2 Duo 3GHz processor, 4GB RAM, 1TB 7,200 rpm hard drive, DVD burner, USB, and Windows 7 Professional 64-bit.
A 1-year warranty applies, although it's unclear who backs it.