Sway bar bushings! My stock styff squeaked like hell before I bought my Aussie Bar. Now the only sound I have from back there is my strut mounts and when I rip the bar from the car.
Originally posted by bk4293:
I'm going around curves it feels like the back end wants to slide over
Slide like the back end is on ice or like the car wants to tip over? Stick your head under the car and look at the endlinks. Checking the bushings that hold the sway bar to the car might be good too.

Though it could always be a loose suspension part (control arm) or your rear end is out of alignment. If you had too much toe when the car loads up one side of the car it would be trying to turn which would make it feel like it was sliding.