Radishes
Raphanus sativus from the Brassicaceae family. Related to the cabbage, brussels sprout, winter cress, mustard, et al. Native to Europe.
These things are a cinch to grow. Simply sprinkle the seeds 12mm deep in a row in any worthwhile soil and off you go. After about 4 weeks, I've gotten like 70-80 radishes waiting for me. Like my eggplants, I've grown them a little too close together so there's definitely over-crowding. Keep them well-watered.
Like my eggplants, my radishes have been a complete success. Still, popular belief has it if you fail at growing radishes than gardening is probably not for you.
I don't have a scanner at the moment at which to scan in photos of my own plants, so I've leached the photos found at Wikipedia's entry for the vegetable. These pictures are copyrighted under the terms of the GNU general public license and are not my own.
The variety I've grown is French Breakfast which are elongated rather than the round variety you'll find at the greengrocer. They have a wonderful crisp and peppery taste which will complement any salad.
I've just picked them straight from the ground, discarded the leaves, gave the root a good wash and ate them straight then and there.
I have my radishes growing in a row between patty pan squash and rockmelons (canteloupes). The creepers and tendrils of those two have started to grab at the radish leaves, but they haven't stultified the growth of them at all.
As a bonus, my pet rats are also fond of the radish, and the leaves of the plant too.