New springs?

Hi
I'm in the market for some new rear springs for my 05 Aveo. Any suggestions on what brand to buy? I'd like some a little stiffer, if possible. Also, how about rear shocks? What do you suggest? Keep in mind I use the car for autocross, which is why I want a little stiffer. Lowered springs are out, as well as coil overs.

Thanks!

I am using Kings Springs and Monroe Sensa Trac Shocks, see my "Garage" for part numbers and measurements.

Thanks! I'll take a look at them.