The Baby Algebraic Geometry Seminar (BAGS) is a joint Harvard-MIT graduate seminar in algebraic geometry; it is distinguished from STAGE by being more focused on "classical" algebraic geometry and less on arithmetic. (There is however a sizable overlap in both topics and audience.) It is scheduled in conjunction with the Harvard-MIT algebraic geometry seminar, whose location alternates between Harvard and MIT.
The Boston University number theory seminar is another research seminar. (The easiest way to the BU math department is probably to walk. Allow 25-30 minutes.)
In prior semesters, BU has also had a student seminar in number theory and algebraic geometry; this may happen again in the future.
The Harvard number theory seminar does not have a separate home page; you can see upcoming talks listed on the math department seminar listing. (Take the red line from Kendall, in which case allow 20 minutes. Or walk up Broadway, in which case allow 35 minutes.)
Informal graduate student seminars often exist at Harvard, but you may have to talk to a Harvard graduate student to find out about them.
Much of the material on this page was taken from the old STAGE webpage developed by Kiran Kedlaya.