George Olsen has developed a persona toolkit, which can help you build detailed profiles of users, their relations to a product (e.g. a website), and the context in which they use a product. The toolkit is pretty extensive, but intended to be based on a pick-and-choose approach.
George Olsen also gives advice on how to collect information. Ideally, personas should be based on interviewing and direct observation, but you can also get useful information from alternative sources, such as domain experts, research, and artefacts that reveal information about the users’ context.