Where can I find a collection of past exams w/ answers on various subjects? I am not currently enrolled in any university (too costly for me at this time), but I would like to study as much as I can in various subjects (Advanced Mathematics, Psychology, Computer Programming and so on.) I'd like to find out the areas in which I am adept in case I decide to attend a university later on in life. This will prevent me from working towards an area that I may not be good at or a line of work that I ultimately find out I'm not interested in (both of which have happened to many people I know.)

Are there any universities that provide past curriculums and exams (with answers) online to be used as study guides?
MIT's Open Courseware project has a lot of material of this sort.  Here is a link to the Course Finder, with courses organized by topic.  The depth of the offering will vary from course to course. Some have only syllabi, others have complete video lectures, homework assignments, exams, solutions, etc.  The coverage is quite broad and includes courses in all of the specific classes you have listed.