While any advice I offer on StackOverflow is free of charge, I do have an Amazon Wishlist for those who desperately feel they want to appreciate my help with something material.
Q&A for professional and enthusiast programmers
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Q&A for professional programmers interested in conceptual questions about software development
Q&A for peer programmer code reviews
Q&A for apps, scripts, and development with the Stack Exchange API