Most 401k plans offer a menu of investment choices.  Some plans are now providing an annuity option- the ability to generate an income stream with a portion of your monies after you retire.  Even if your plan doesn't provide this option, you'll have the ability to rollover funds into an IRA and buy annuities.

The Saturday Wall Street Journal provides some tips, advice and a podcast on annuities.

A number of companies are introducing products that for the first time allow workers to invest in annuities through their 401(k)s, the heart of many Americans' retirement savings. A 401(k), for the most part, is easy to understand and set up. But it doesn't offer a simple mechanism for creating a steady income in retirement. Annuities, by contrast, have long offered a way to generate a paycheck in later life but tend to be complicated, expensive and a general pain in the neck to shop for.