How can I narrow down my CS research interests when my undergrad institution doesn't have a large CS department?
I'm in an analogous situation. I'm one year out post-undergrad, and am applying to programs this month as well. I also came from a relatively small program, and didn't have a great idea of what direction I wanted to go in.

What I did (and this is perhaps not the most efficient), is I went to the webpages of some schools I was considering, and looked through all of the CS faculty's personal pages. Be forewarned, many of them are badly designed, but a lot of them also have a short description of what the professor's research is about, in their own words. From these descriptions, I started to get a better idea of what did and did not interest me, and it gave me specific people to mention in my applications. 

Of course, this approach relies on you having a relatively small list of schools that you're considering. If your list is more than 20 or 30, I could see this becoming too much, or if you have no idea where to start, it might also not be great.