ES Suspension

What could I do to improve the suspension of a stock ES?

Would you accept some added ride harshness? If so, a set of Eibach Prokit springs would improve handling. H&R springs may improve handling but with less ride harshness. Depending upon how many miles are on your odometer, you might also consider replacement shocks. I love Konis but am not sure if they are available for your car. Coilover suspensions (high cost) may be overkill for a car of that age. Lastly, a beefier anti-sway far up front typically improves steering response.