Astronomy Colloquia - Geared towards astronomy grad students and faculty but good for upperclassmen and especially those who do research in related fields. Followed by wine and cheese with the guest speaker in 1402 Pupin.
Physics Colloquia - Most are not too accessible but occasionally there are good astrophysics or big physics results that are fun to hear about. Preceded by coffee, tea and cookies with the guest speaker at 3:30pm in 705 Pupin.
Astronomy Seminar - Highly specialized talk not recommended for anyone but the most adventurous undergrads.
Pizza Lunch - Pizza is $1 dollar per slice and various faculty and grad students will discuss latest results from their respective sub-fields.
Public Outreach Lecture - Geared for the general public but great for students especially if you want get less scientifically inclined friends to appreciate astronomy. Followed by public observing on the roof.
Astro-Ph Coffee - Grad students share the latest from astro-ph at arxiv.org while enjoying coffee
Astro-Ph Beer - Kind of like Astro-Ph Coffee but without the coffee.
these events are for undergrads, by undergrads