I've written a lot about my large magnet board. (It's really an oil drip pan from the automotive section of a discount store.) We use it with magnet shapes and magnet sticks. We use it as a magnet table. We even use it for sticky paper play. (Note: Check out my post on Pre-K Pages about using the large magnet board for graphing.)
But I haven't mentioned our small magnet boards. These are also repurposed items - stove burner covers. These are square but I've seen circular ones, too.
We bought them a while back. (Sometimes you can find them at the dollar store or other discount store.) We pull these out when we want to have more individual magnet experiences or use a table but not the whole table (as with the large magnet board).
We've used magnet shapes and magnet letters. We've used magnet figures (to retell stories or play out original stories). We even had eyes, noses, and mouths to make funny faces.
These are great resources for centers or smaller areas for magnet play.
I really like these because you can use them as dry erase boards, too. And, if you flip them over, they make great trays for holding all kinds of things. I like when I can get lots of use from something!