You can use one of these PoE injectors.
Value Gigabit 802.3at, 30W (PoE Injector)
Ubiquiti Instant IEEE 802.3af GE Adapter (PoE Injector)
Another 802.3af or 802.3at model would also work. :-)
If you don't have one yet, you just need an RJ45 cable.