Great question. There are a number of retirement options that S-Corps and small businesses can take advantage of. In addition to the Simplified Employee Pension (SEP) Individual Retirement Account (IRA) that you mentioned, S-Corps can also take advantage of 401(k) plans, Savings Incentive Match Plan for Employees (SIMPLE) plans, profit sharing plans, money sharing plans, and other savings plans. Information about some of these options can be found here.
I hope this helps you find some good new options to explore.