http://www.nikonchat.com/nikon-flash-d60/

What is the cheapest way for me to use wireless TTL flash with my Nikon D60 and SB600?
The Nikon D60 does not have the wireless flash commander-in-camera, so the D60 popup flash can not do wireless TTL flash itself. To make wireless TTL flash with the D60, you have add one of the following: 1) the SU-800 commander flash, or 2) the Speedlight SB-800 flash in the shoe, or 3) the new Speedlight SB-900 flash in the shoe. The SB-800 SB-900 flashes commanders have wireless flash, so you can monitor an SB-600 off camera wireless TTL. The SU-800 is designed specifically for the control off-camera flashes.
Nikon D60 Full Review Pt. 2