The ways to get user personal information (but not confidential)

I want to implement clever personalization on my website. So the site will change it design and behavior with respect to user type. I know how to make users clusterization, but we don't know where to get data that can characterize the user. I know that I can use:

1) http-headers that web-server will get from the user browser
2) Some questionnaire form that I can ask user to fill with questions like age, gender, etc. But users very dislike to fill this forms and can leave from site because of this

What are others possible ways to get user personal information? Maybe from some external systems like search engines (they have such info and using it), or maybe from Microsoft. I don't need any confident info. I can't find any info that search engines or other web-services provides this info even for money. Maybe you know such systems? Maybe you can advise other ways.