Nolathane rear subframe bushings. This was my first suspension mod, looked at all the options and it is by far the best solution out there. Cheaper and easier to install than the M3 rear subframe bushings.
As with everything on the car this was a DIY. With the help of an indestructable PVC pipe, I pulled out the bushings with just hand tools.
Heres the full thread
http://www.1addicts.com/forums/showthread.php?t=1158856
Really locked down the rear end and stopped the car from steering all over the place when under power. These soft bushings are designed to work with the stock runflats and I did find the harshness over sharp bumps to be more pronounced (I still had runflats on the car). Very good value bang per buck mod if you can find someone to install them for a reasonable price.