Is there a subforum on StackExchange specifically for math students who have questions about course suggestions, preparation for grad school, etc.?
Update: it came to my attention that graduate admissions are on topic at Academia.SE. See in particular
- Path to a good grad school?
- Acceptance into graduate math programs
- What advice would you give students applying for graduate school in mathematics?
At present, there is no SE site for undergraduate math career advice. As you probably noticed, Academia.SE is for graduate school and above.
There is a proposal for a site Higher Education:
Proposed Q&A site for questions related to higher education, high school, college and grad school admissions including preparation of standardized tests like GRE, SAT.
The proposal hasn't had much support yet. It's still in the "definition" stage, 11 months after creation. And the example questions appear to be mostly of "preparation for standardized tests" variety.
One issue is that suggestions of courses to take will be specific to your institution, and preparations for graduate study is something that should be tailored to your strengths and weaknesses. An SE site can't replace an academic advisor (I presume you have one).
I think this site may be helpful to you, if you don't know it already: http://www.mathematicsgre.com/