401k Retirement Plan
A 401k retirement plan should be the first savings you consider when planning for retirement. 401k plans are often backed by employers, who usually contribute thirty cents or more for every dollar you contribute to your plan. Often you'll have various mutual funds to choose from--some which are more risky and some more secure--so you can invest in what's right for you. Finally, you don't have to pay taxes on the money you contribute to your 401k until you take the money out during retirement.
These pages will help you get a basic understanding of what a 401k plan is: