Kohlrabi is an interesting brassica-family crop that looks like a root vegetable, but the bulb grows aboveground rather than below. We're fairly new to growing kohlrabi, but we grew kohlrabi in our Central Texas garden last year with great success. You can grow them from seed or from transplants, and kohlrabi is cool because the entire plant is edible, and can be eaten cooked (think roasted - yum!) or raw (think slaw - also yum!).
One thing we learned is that you want to harvest the bulbs when they're about 3 inches in diameter or less. They're still edible if you wait longer, but the bulb gets tougher and isn't as tasty.
We grew two varieties last year - Delicatesse White and Blauer Speck.