So, Dan, being the guy he is, proposed a piece of sheet metal. I already had the white board from Lowe's for $10 for the whole 4'x6' piece. He drove to a local fabricator's shop and showed them what he wanted to use the sheet metal for. They were all familiar with our local science center's board and knew exactly what we wanted to do. They hooked us up with a 25 gauge piece of sheet metal for a mere $40. And it's big enough for four kids to use and not fight. Awesome.
Simple phonics magnets from Leap Frog- these tell you the word you spell or the letter you put in the little computer part

Good ol' fashioned magnetic letters in upper and lower case. These are nice and big. I got them from Discount School Supply.

Magnet wands with chips and balls- these are also from Discount School Supply (these are used on the floor)

The magnetic wall. It's 4' x 8'. Yes. We are absolutely the kind of people that will nail a honkin' piece of sheet metal to their wall. We've been discussing an addition. The metal walls stays. Or gets put back. I'm just sayin'.
I'm putting these in a few box categories depending on the magnet set. Lots of good letter recognition and science here. Any of these would be a welcome break in the middle of doing seat work activities from the boxes.