So I was bored and surfing the web when I StumbledUpon the following:

100 Free Online Ivy League Courses You Should Take Just For Fun

Browsing the list of courses, I began to wonder: "How is this possible?" A bit of Googling led me to a page on the MIT website, which had this to say:
MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity.
What is MIT OpenCourseWare?
MIT OpenCourseWare is a free publication of MIT course materials that reflects almost all the undergraduate and graduate subjects taught at MIT.
  • OCW is not an MIT education.
  • OCW does not grant degrees or certificates.
  • OCW does not provide access to MIT faculty.
  • Materials may not reflect entire content of the course.
How do I register to use MIT OpenCourseWare?
There is no registration or enrollment process because OCW is not a credit-bearing or degree-granting initiative.
Can I get a certificate?
No. MIT OpenCourseWare is a publication of the course materials that support the dynamic classroom interactions of an MIT education; it is not a degree-granting or credit-bearing initiative. However, you should work through the materials at your own pace, and in whatever manner you desire.
List of MIT OpenCourseWare classes by department
And apparently there are similar programs at a number of high-profile universities. Here's a handy site that I found to navigate through it all:
OpenCourseWare Finder

I am very excited about this. I am graduating from college in May and there are a few courses that I regret having not taken, due to schedule and/or credit conflicts. With this OpenCourseWare stuff, I can learn as much or as little from those classes (and many more) as I see fit. I'm pretty busy with school currently, but I plan on doing some of this over the coming summer.

Enjoy!