In a ~fancy~ place like Princeton, a no-frills dive bar is much appreciated, and Ivy Inn delivers. The patio is a great place to be on a warm evening, though it can get crowded later in the night.
Cheap beer, karaoke, and full of townies. Bring in food from George's or Old World Pizza next door and reminisce about all the times you used your fake ID here during winter break in college.
Come for trivia on Tuesday's, sit in the back patio, play some corn hole and enjoy a chicken cyp from George's next door (they let you bring food in)...complimentarypopcorn as well!
Not a very good version of a dive bar. However, I did see a really tight Led Zeppelin cover band once that rocked pretty hard (but annoyed the hell out of everyone I was with). I hope they come back.