What is a good replacement for the rear springs?

From RPRWiki

You have two choices. The best, and more expensive choice is to buy coil overs from Ground control, KONI or OPM. The cheap choice is to get a set of Integra or Civic Wagon springs from the junkyard and cut a coil or two off of them. EDIT: recently the Acura RSX (aka Honda Integra 2002-2007) springs have been found to work for the 1g crx and 3g civic but, like the wagon and 1g integra springs, they will need to be shortened to retain a stock or lower height. The RSX spring rate is comparable to the aftermarket coilovers at a fraction of the price.

Also to mention, the Eibach springs sold for the 1/3g are a progressive design that is pretty much worthless for sport driving.