Bank of America has an ATM in the Student Agencies (not student services as mentioned before by Islander4 although I thought that it was student services as well lol. Student Agencies, Inc. - Collegetown Student Services
) building in collegetown, near Collegetown Bagels. The main branch is in the commons (ez walk down, but loooong walk up that hill)
Tompkins County Trust and CFCU have mini-branches at the Cornell Store. TCT (or maybe it was M&T....) has an ATM in collegetown as well, (across from starbucks)
M&T is in collegetown as well (near starbucks)
First Niagara (formerly HSBC) has a branch in the commons and an ATM at Willard Straight Hall (WSH, across from the Cornell Store)
WSH also has another ATM, don't remember which
I personally used HSBC but have recently begun using Bank of America. Their online banking is super easy and also pretty common along the east coast if you're planning on doing internships.
I don't remember ever encountering "traffic" at branches/atms at all.