Upper-division math courses are available online from various universities, with MIT's OpenCourseWare and Berkeley's Math Course Archive being notable resources. In addition to these courses, users are encouraged to explore authoritative math blogs and articles, such as those by mathematicians Timothy Gowers and Terence Tao, as well as the Scholarpedia for reliable information. While Wikipedia can be useful for keyword searches, it is advised to rely on more credible sources for in-depth study.