Craigslist TOS says we are prohibited from using their data if we ourselves are providing classified services. I looked around and found that all sites that were asked to stop their use of Craigslist data were sites that were constantly scraping the site to populate their own database. The way we see it, a user searching on our site, and us querying CL, is no different than that user directly searching on CL. We're querying them per user search.
I just remember other sites (like Housingmaps.com) being exceptions because they were totally non-commercial. I didn't actually read their TOS until now. It looks like you're definitely in violation of their TOS.
They might not really care or notice unless you grow though.
I'm not sure that will stand for long:
Edit: I should add that I like what you guys have done. Congrats on launching.