Hellobee Boards

I have this exact one. It's great, no complaints at all. We got it for DD's first birthday and she still plays with it as a preschooler. We had it filled with both sand and water but it got really messy (think the whole thing full of muddy sand) so now it has sand on both sides.
Eta: we have a separate water table

I thought about getting a dual water/sand one, but was worried about it getting messy and gloppy with wet sand.

We have this water table and really like it. Owen loves it and it's interesting enough that he's even played with it without any water - just putting the balls down the center chute, moving them around the little ferris wheel thingy, etc.

http://www.amazon.com/Little-Tikes-Spiralin-Seas-Waterpark/dp/B004INDQWY/ref=sr_1_2?ie=UTF8&qid=1367955033&sr=8-2&keywords=water+table