Wow, thanks so much!
Yes, I totally forgot to mention the writing sample. I've got a research proposal I did for a class a semester or two ago, which I'm going to rework this summer. Ultimately, I'd like to do the actual research through a UROP program, but of course I won't have that done by the time I submit my applications.
The small research project I'm doing is a 2 credit independent study. I would love to do more, but this professor wasn't looking for anything big, so I settled for 2 credits. =\ Like I said above, I'm really hoping to do a UROP sometime this year...or an honors project (which I guess is basically the same thing as a senior thesis, since apparently my major doesn't do senior thesis at my school). So, if I don't get accepted this year for grad school, I'll probably reapply next year after I actually graduate and have more of this done and more research experience. But I might as well try right now, anyway.
Yeah...this is the part I'm most nervous about. I'm doing a (required) internship this fall, but it's with an outside, small-ish organization. I'm sure I could get a good letter of recommendation from my supervisor there, but I don't know if that's absolutely the best idea since she's not a professor. But, if I got one good one from a professor, another good one from my internship supervisor, and another mediocre one from another professor, that might look better than one good one and two just-ok ones from all professors.
Anyway, thanks for all your input, I really appreciate it!