New independent contractor - tax/retirement advice please

[yoga mama]

My husband is just starting to do some computer programming for an acquaintance.  He will be working as an independent contractor.  We hope to invest as much as possible of his earnings into a retirement account, and are unsure as to whether we should do a SEP IRA, simple IRA, or 401K.  We also want to plan appropriately for taxes next year.  He has been a stay at home dad with our kids for a few years and we have been filing married, filing jointly.  My income is around $300K after retirement contributions.  I might guess that he would earn $15-25K this year.  If you have specific advice for me, I would appreciate it.  If you can refer me to a great resource on learning about finances as an independent contractor (book, blog, etc) I would appreciate that too!  Thanks!

[terran]

A solo 401k will be the one that lets him sock most if it away at lower income levels. The others are limited to 25% of his income, and they're all limited to ~$53k or something, so at high income levels it doesn't really matter, but at low levels you can put in that 25% on the employer side plus up to 18k of what's left over into a solo 401k. Here's a calculator you can play with: http://www.bankrate.com/calculators/retirement/self-employed-401-k-calculator.aspx