One of the big challenges when preparing for the listening and speaking sections of the TOEFL iBT is the lack of easily accessible study material. Thankfully, elite universities across the world are podcasting their lectures for free over the internet! This will allow you to use their materials to simulate an actual iBT environment.
Thanks to Open Culture for compiling this comprehensive list of university podcasts.
Keep in mind that the 2-minute lectures presented on the actual TOEFL are engineered specifically for the exam, therefore they make their points very clearly and quickly. The actual lectures available on the internet are not necessarily going to be as concise as what you hear in the examination.
When studying, keep a timer nearby and summarize the 2 minute segments of the lecture. it is critically important that you get comfortable in the actual testing environment. The passages in the speaking section are up to 2 minutes in length. Then you will get 20 seconds to prepare a response, and 60 seconds to summarize. Good luck!