The colleges that sent me mail! I'm old school, I read at least the first paragraph of my college mail I get and if it strikes my fancy I'll research the school online, get on their mailing list, visit their CC forum
ect. I discovered University of Chicago this way and its my top choice!
That being said, rankings, both general and interest-specific, do help roughly get a list going, Wikipedia is a good source of random, unbiased info on Unis, and actual college websites are great too! Also, try using PR's Counselor-O-Matic (completely ignore their safety/match/reach recommendations though). And finally, and I can't stress this enough, TALK TO PEOPLE! People who have gone through the process are treasure troves of information. I have an aunt who's eldest son was going through the admissions journey three years before me, and shes been the go-to person for questions and has also opened my eyes to other schools that she deemed would be a fit for me. This is how I discovered Swarthmore, another school I love. People who know you well, have gone through the process (especially with an applicant with similar stats and aspirations as you) and who know you well are the best sources.