If your employer offers a retirement plan, like a 401(k) or 403(b), and will match a percentage of your contributions, you should definitely take advantage of it—after all, it's free money for you. Plus you'll have a tax-deferred account that makes saving a cinch through automatic payroll deduction.
If your employer doesn't offer a plan, then an IRA can be a good start to your retirement savings and another opportunity for your earnings to grow tax-free.