Residents of some border states (WA, MI, NY, VT)and some Canadian provinces (BC, MB, ON, QC) can also obtain "Enhanced Drivers Licenses" that can be used as entry documents at land and water crossings. A US Passport Card is also convenient if you're prone to forgetting your passport. Nexus can also be used between many US and Canadian airports. Nexus holders can register with US Global Entry just by checking a box on the application.
My favorite Nexus benefit is avoiding hours of waiting in line at major US/Canada border crossings, especially on holiday weekends.
One potential drawback for some people is that applicants to Trusted Traveler programs receive a criminal background check.
Yes, you need a passport these days (or a Nexus pass if you're a frequent crosser). It's new, and it's mostly because Canadians need a passport to enter the US in the security theatre aftermath of 911. Until recently all you needed was a birth certificate or citizenship status card to go either way; the visa was implicit.
