I plan on applying for an REU program this summer. I know my research mentor will write a very good recommendation, and is well-known in the field. However, I have no other connections. The applications are due in March, so I think I shouldn't place too much stock in next semester's professors. I don't particularly like the professor of my only "major" class (ChemE), but I do like my math professor and have had him for two semesters (albeit, I don't go to office hours or speak up in class, but I do well and he knows my name). Should I start attending his office hours just for this purpose? Or should I suck up to my ChemE prof? OR, is it acceptable to get a graduate student or postdoc to write a LOR? Both of these see me every day in the lab.