Servers are cheap, but used servers are even cheaper. Vibrant Technologies buys, sells, leases, and repairs new and used servers and other storage and networking hardware at a 20-80% discount off manufacturer's list price. They will also buy your used hardware.
Their web site says:
All refurbished equipment is fully tested, configured and packaged to the manufacturer's standards. Leasing and short-term rentals are available. We are also interested in your trade-in and excess equipment. We'll give you top dollar for your hardware assets. Source
Their midrange server products include HP, IBM and Sun. They also provide networking and storage equipment from Kingston, Seagate, Quantum, Dataram, Clarion, Exabyte, ATL, and Phillips. Learn more at www.Vibrant.com.