Every other summer, the Linguistic Society of America holds a sort of summer school, traditionally known as a "Linguistic Institute". The 2011 Linguistic Institute was held at the University of Colorado at Boulder; the 2009 Institute was at University of California at Berkeley; the 2007 Institute was at Stanford; and so on. The courses at each Institute are taught by faculty from around the country and around the world, and the students are similarly diverse. Enrollment is open to all.
The 2013 Linguistic Institute will be held at the University of Michigan, 6/24/2013 to 7/19/2013. Its organizers, Andries Coetzee and Robin Queen, have issued an open "Call for Course Proposals", inviting members of the public to add to the existing list of proposed courses by suggesting "exciting, dynamic courses … that are devoted to new lines of inquiry".
They explain that
Our aim is to develop a set of courses that provides broad coverage of linguistics and that captures the Institute theme of “Universality and Variability.” Each course will meet twice a week for four weeks, for a total of 8 meetings; each class meeting will be 110 minutes long.
Proposals will be evaluated by the Institute Steering Committee, which will make the final selection of courses.
The call gives a detailed specification for what a course proposal should contain. Since the requirements include not only the plan for the course, but also details on who would teach it, the solicitation is aimed mainly at potential instructors. If you're a potential student, and you have an idea for a course that you'd like to take, and you don't see on the existing list, you'll need to recruit someone to teach it as well!
I attended a couple of Linguistic Institutes as a graduate student, and taught at couple of them later in my career. Like most others who have participated, I recommend the experience. Quite apart from the content of the courses, It's a terrific way to get to know a spectrum of interesting linguists.
[Full disclosure: I've been invited to teach at the 2013 Institute, and will do so if my (still uncertain) schedule permits.]