There are now graphite impregnated poly bushings that get rid of the squeaks.

Energy Suspension makes good stuff. I don't know if it's graphite impregnated, though.

http://www.energysuspension.com/index.html

Performance Suspension makes the graphite impregnated bushings.

http://www.performancesuspension.com/polymainpage.htm3

Don't know whether it's worth the extra cost unless you're building a canyon carver.