Scattergories game -- works for individual players or teams.
This can actually keep you going for quite a while... and it's fun to see what the students come up with. I teach in a middle school, and had to laugh when a group put down "romance" -- for "things that are hot" that start with "R".

I've used letter dice from a Boggle game to choose the key letter for each round, but I kind of like choosing the letter myself better. Then I can choose starting letters the students tend to have the most difficulty with (R, L, P, F, etc.). When I call "Time's up!" at the end of each round, one student from each group writes their answers on the board (while I check to make sure they're ONLY writing what was on THEIR team's paper). Then we go over the answers, crossing off words that more than one team had, words spelled incorrectly (we also go over the correct spelling), words that don't fit the category (sometimes go over
why they don't fit...), etc.
I've attached a couple options -- a PPT version of the game as well as a paper list format that you can print out, cut up, laminate, and hand out to each group for each round.
Enjoy!