Over the last 4 years, ATLAS has taught hundreds of TOEFL iBT students. After each student takes the test, we do an exit interview and ask them about their experience.
We usually record the topics for the speaking questions in Task 1 and 2. These topics fall into 6 big categories or 30 subcategories. These are represented in the area graph. The bigger the square, the more common the topic. You can click on any of the topics to download our material for that topic (or read a list of topics here).
If you are taking your TOEFL test soon and only have a little time, I recommend starting with the big squares. However, if you have lots of time, work on items that have the same color. For example, do all the red squares, then all the green squares, etc.
There are a few surprises here. For example, "Restaurants" are a very common speaking topic. A typical question is "What are the characteristics of a good restaurant?" This can be a little tricky (but very easy if you review our material.)
Here is Another surprising question - "Is TV bad?" This question seems to come up again and again (and many students find it difficult to answer.)