There's really no reason that a pot filled with soil can't sit next to your computer, but something about a hydroponics system just feels more thematic.

Desktop Hydroponics, available for $40, is a means to grow herbs at your desk. Essentially a plastic shell with some sponges and nutrient mix, its slot-type top should hold stalks in place...while tempting your coworkers as a means to dispose of old CDs. [ThinkGeek via UberReview]