You can set up a solo 401(k) if you are self employed. For 2005, if you are under 50, the maximum contribution is $42,000, or your total income, whichever is less. You can design a plan that allows all or part of the contributions you make be ROTH contributions, if you want.
The IRS publication for setting up retirement plans for small businesses is at http://www.irs.gov/publications/p560/index.html
I like the web site JDW posted for 401(k) information. It also provides links to possible providers.