I lowered mine by 30mm's with Eibachs. Their website says that they're designed to work with standard shocks, and I beleive that this is the case with many spring kits.
Mr 6 is right in saying that labour-wise it will be cheaper to do springs and shock together, but this is only really a saving if the shocks actually do need replacing. Your car's not that old, so they might not need doing, but depends on how much mileage you've done.