We have been making Play Dough seasonally, which seems to work out well. We choose a different color and scent depending on what we are exploring for the season. This Summer we chose to make Yellow Play Dough with Gold Glitter and Coconut Extract (it smells like suntan lotion and the beach!) I rotate out the cookie cutters and stamps to make them seasonally appropriate as well. I also try to put out some letters to write a "word" that would fit with our theme.
You can find the Recipe here: Play Dough