Countertop space is often nonexistent in small kitchens. We use Ikea's Lamplig chopping board to add about 3 sf of space to ours. The board is just the right size to cover our sink, so we can use that space for a prep area when the sink's not in use. We turn it opposite of what's shown in the photo, so the flange of the board catches the front edge of our countertop and holds the board in place.
It works out well, though the maple board is only 3/4" thick and tends toward warping. We stay on top of that by oiling the board frequently to keep it sealed against moisture. We've seen custom boards made to fit over kitchen sinks, but we're happy with this one at only 10 bucks.