Freelance taxes

Does anyone here do freelance and have experience with the taxes involved? I've just started contract work for a guy on my free time, and will probably trigger the $600 form 1099 level. How much should I set aside for taxes? I work a part-time job as well, and have student loans and scholarships, but I've only had to file a 1040EZ...they just ignore the school stuff. But what should I worry about for taxes come next year?

Thanks!