MIT's most iconic building appears to be the Great Dome (shown below). If you do computer searches on MIT and the Great Dome, you'll likely find a lot on "Hacks" (i.e., pranks) done in conjunction with the Dome, including putting objects on top of it.
Shown next is MIT's Wiesner Building, an I.M. Pei designed edifice that houses, among other units, the school's Media Lab.
Finally, in walking around MIT, one of the neatest things, in my mind, is the panoramic view of Boston you can get from the Cambridge side of the Charles River. In the shot below, you can see Boston's two skyscrapers, the John Hancock Tower (another Pei design) on the left, and the Prudential Tower on the right.
