Math.
You want to know what's crazy? I think I'm going to miss taking higher level math classes a lot when I'm teaching. Maybe I will take summer classes once I'm finished with my education masters and get a masters in math over a couple of years... not necessarily because I want to use it, btu because I love it. Is this crazy? It will probably help me when I'm applying to get my Education PhD 20 years down the line, eh? And does your salary increase when you take more masters credits? I don't know these things, but either way I'm going to take the classes. I love math!