This is what I used on mine.
Link. It's syn, and also works great on your brakes. I'm going to be putting on my front Si bar next week (it's sitting in the garage and killing me to look at it everyday). I put lots of it in the bushings and on the ends. My rear Si bar has been on for some time, and it's still quiet as can be.
Also, like was stated earlier, install it when the suspension is loaded, or you will have noise!
Brian