I am an even bigger fan of partner cooperation. There is something about a group of three or four that makes me feel like someone is probably getting lost in the interaction. When you are working with a partner, you are directly accountable to one other person. I even have my students seated as partners.
I learned my favorite partner practice from another teacher in my grad program a few years ago. I found out later that it is a Kagan cooperative learning structure called boss/secretary.
Student 1, Boss: This student's job is to watch and tell. Student tells how to solve the problem, and describes each step with enough detail that the partner can get it written down. This student should be talking and watching, but not writing.
Student 2, Secretary: This student's job is to listen and write. Student writes down the solution as the partner describes it. This student should be writing but not talking. The exception is if the partner gets stuck or makes a mistake. Then the student can coach and assist with the solving.
What I like about boss/secretary: It can be done at any time at the drop of the hat. It can also last for any length of time. I will often stop in the middle of a lesson and check for understanding this way. I will just throw out two problems and tell the person sitting on the right (or wearing the most green, or the biggest feet, or the oldest . . .) to be solver of the first problem and then switch roles. I also just used it for a unit review that lasted a whole class period. We used white boards and I signed off on each section as it was completed.
What I don't like: Students have to stick to their roles in order for it to be a meaningful interaction. I have seen students who are responsible for listening take charge of the problem, or students who are in charge of talking to take a passive role. It is helpful to have students switch roles with every problem.