See the various versions of The Nutcracker... We have the classical version, the Urban Nutcracker, and the Slutcracker :) Google all...
Go ice scating on the Frog Pond or on the Kendall Square outdoor rink.
Look up chocolate and cupcake tours of boston - those are always fun!
Go Salsa Dancing :) Salsaboston.com has good info.
the Institute of Contemporary Arts and the Museum of Fine Arts are always good.
Boston.com has good info in the "stuff to do" section.