Tape one large piece of paper for each student on the wall around the classroom. Give everyone a colored marker and have them stand in front of their papers. Ask everyone to write their topic in the center of the paper and circle it.
Now, have everyone rotate so they are standing in front of someone else's paper. Allow 30 seconds for students to write everything they can think of about the topic, using a mind-map style web. They can ask a question, add a subtopic, make a comment--whatever comes to mind.
Rotate again, and keep going until everyone has had a chance to respond to everyone else's topics. You will need to extend the time as the papers fill up, because it will take students longer to review what has already been written.
If you have a small classroom with no space for the paper on the wall, this activity works just as well using large paper (I used 11 x 17) passed along desktops. If you can, though, use the wall because it's a great opportunity to get students up and moving, and if nothing else, it's fun to write on the wall.
At the end of the activity, each student can take their own paper and see what everyone else has to say. Perhaps they will find an interesting question or a direction they hadn't thought of before. My students find it very helpful, and some even switch topics to something else they found on the wall that seemed more interesting.