I'm reading a book for a study at school called
Explicit Direct Instruction. The authors say you should always call on a "non-volunteer" after posing the question and waiting for think time. I've used this technique and the term non-volunteer since the beginning of the year, and I STILL have hand raisers. But now everyone knows I'm not going to call on those people unless I draw their stick. Before using this strategy, I had 4-5 people who totally dominated every discussion every day -

- and I'm not exaggerating. It got so that no one else even tried to answer which probably meant that no one else did much thinking either.
BTW, I have my students for 2 years, so I knew I needed to do something or else the other poor kids would never get a chance!!!!