cnet newsblog has an article about when used servers cost most than new

GALWAY, Ireland--Think of the Multis Group as sort of the Antiques Roadshow of the server world.
The Galway, Ireland-based company specializes in refurbishing, and then selling, used servers. Refurbished PCs and servers are increasingly in vogue because remanufacturing represents a more environmentally efficient way to recycle old electronics than harvesting components from these old machines or melting them down for raw materials.

Multis, in fact, plans to open a 70,000-square-foot facility in Union City, Calif., later this month to refurbish and sell servers for North American customers. That marks a reversal in the usual U.S.-Ireland tech relationship.
Unlike refurbished PCs and cell phones, servers maintain a high resale value that can equal or even exceed the cost of new equipment, said Multis CEO and founder Sean Keenan. Why? Manufacturers might produce only a single server model for 18 months to two years. Corporate customers, however, often don't want to migrate to new hardware that quickly. Instead, they move at a three- to seven-year pace. As a result, they often have a need for discontinued equipment.

People should consider contacting Multis to discuss end of life for their servers and an eWaste plan as part of creating a green data center.