Using their Lecture Browser, you can search for any phrase or keyword and quickly be presented with all of the lectures that used that specific term. Here is the very cool part. Not only are you shown the exact paragraph of the transcribed lecture, you can also watch the video of that exact potion of the lecture, on demand and for free.
My explanation may not do this any justice so here are a couple of images to better explain. If I were you, I’d just go check it out. You’ll catch on in about 10 seconds.
I entered “Chicago” as my search term:
The lecture started and I was able to watch/hear the entire thing.
Below the video window (not shown here) was a text box that underlined each word as the lecturer said it. So if your some reason you can’t hear the audio, you can still follow along.
By the way, it’s worth noting that although you associate MIT with technology, you can search for terms within different subjects such as Biology, Media, Speech, etc.
Check it out at the MIT Lecture Browser.