You sound like quite a unique candidate. I'm willing to bet actual money that if your grades are decent, you'll be a shoo-in to any B.Arch program.

For the love of cross-disciplinary art+architecture, please tell me you're applying to RISD and the CCA???
Carnegie Mellon also has both a strong graphics and strong arch undergrad program... also encourages cross-disciplinary studies...
Syracuse, Cornell, USC, SciArc, Cincinnati also all strong B.Archs... I probably missed one but those are the ones whose graduates and student work have impressed me...

Oh, and the answer is two-fold :
you need to do what speaks to you most. There's no one "target" item to have in your portfolio or in your experience -- the most important thing is to discover what moves you personally, what motivates you, what excites you -- and pursue that. If you pursue some activity simply for the sake of pleasing some hypothetical admissions reviewer, and your heart isn't in it, it won't shine anyway.

So, whether it's one single project, or volunteer work, or whatever -- it doesn't *matter* what it is as long as it grabs you.

That said -- in general I would try to make your portfolio well-rounded. So, if there happens to be some area you think you're lacking in, AND it's something that moves you, then pick that over something else that moves you that you've already done.

ah, forgot Kentucky & Kansas.

But in terms of a true multi-disciplinary, multi-platform/media architectural experience, in my opinion your best bets are RISD, CCA, and CMU.

Thanks for your response. You definitely mentioned a few of the schools I was checking out– I'll say for now that I was not able to meet CMU's deadline (December 1st, I'm still working on my portfolio and getting my recommendations written).

I'm sure I'll have to find something that really gives me an opportunity to do whatever I do best. I'm still undecided but I expect it will be more clear as opportunities pop up and some of my rougher ideas start grabbing my attention.

As far as recommendations, I wonder what everyone thinks of this. Of about five people, there are three who I was considering for my architecture apps (Columbia + Harvard being the only non-arch undergrads I'm applying to): my psychology teacher, drawing/color teacher, and the studio owner where I interned. Psychology is a bit of an odd one, but I thought it could be handy since I did very well in the course, it's an academic subject, and a big part of my process is understanding how my work is meant to make people feel and interact. The only downside to my school situation is that being at a college and driving 50mi every day to get there doesn't give me much time to really know any of my teachers– the people I asked were those who I was most friendly with outside of the classroom with, and made an effort to inform them of the things I'd been doing since taking their class(es).

Of the three options that you mentioned, the most important thing that you could do is add more artistic items to your portfolio... From my experience talking with Cornell B.Arch professors and successfully applying to the school, it seemed as though what they were looking for was basically evidence of creativity in some form of visual work. I would say that you should go for breadth of projects rather than focusing on a single big one, because they might not like the one big project.
Overall, you sound like a really strong candidate... good luck!