I use numbered heads and the Showdown strategies a lot in Reading and Math. In fact, I've used task cards I have printed from here on PT for Showdown. I also recently used Rotating Review where the kids worked in small teams to come up with different Proper Nouns. Basically I had 6 catagories on chart paper posted around the room and kids in groups of 3 with a reporter, checker, and recorder. The recorder wrote for the team, the checker made sure they were not repeating another team's answer, and the reporter added up the points they scored each "round". They had 2 minutes to come up with as many proper nouns to match the common noun given, i.e. Restruant, then they moved on to movies, etc. I don't always have specfic roles for the students when they work in groups, but this activity I did.
I also have my kids work together in teams to create projects like a gameboard or even a business plan recently. I also gave them pictures of different parts of a skeleton and had them counting bones in groups.
There really are no bounds when it comes to group work. I also pair them up a lot for think-pair-share. I use whole brain teaching's Crazy Professor Reading where they read in pairs or small groups and question eachother as well as literature circles. If you need more specific ideas, let me know! I have lots of materials and there is no use in recreating the wheel.