I wrote about the construction of our salad tables back here. We have several kinds of lettuce, spinach, green onions, cauliflower and broccoli planted in them. (Probably some other things too, I forget at the moment.)
They seem to be particularly nice for early in the season planting in our area. Keeping them up against the house seems to keep them a lot warmer when it freezes at night (though I tuck them in under old blankets when it freezes - we've had a week+ of above-freezing temps at night!). I'm still experimenting a bit with things. I'm guessing that some of them (especially cauliflower and broccoli) will have to be transplanted into the bigger garden before they're fully grown. Also not quite sure if we should have packed the dirt a bit higher. Guess we'll be learning a lot about gardening this year!
Here's what they look like today: