This article offers good insight on business models for web freelancers. The primary considerations is “Base pricing decisions on the service you want to offer, and who you want to offer it to”. Working strictly on an hourly rate has drawbacks and affects design decisions in that clients may feel like they are getting nickeled and dimed everytime they consult with you. So you may want to consider a weekly rate or a flat project rate. When you look at project rates be very careful on spelling out the project scope in writing. Another consideration is support. What will you offer and what is the cost.
Rachel Andrew founder of edgeofmyseat.com, the company behind Perch CMS discusses business models in light of her experience. This article also includes links to rates others in the design and development community charge. Note that the links are for EU businesses which differ from those based in the US.