Hmm, well so far, I have one science professor who said he could write me one (and he's one of the few science professors that I've spoken to semi-frequently outside of class, so he knows me fairly well). I am going to ask my 2 current science professors, as well as my public speaking professor. Out of these, the public speaking professor is the one who knows me the 'best'. I'm also thinking about asking one from one of the semi-heads of a (non-science) organization I'm a part of (she already offered to allow me to use her as a reference), though I'm not sure what 'category' of letters this would fall under.
I just have to ask.. is there a limit to the # of LOR's you can submit to pharmcas?