Cress (or mustard) is probably the easiest thing to grow yourself if you don't possess green fingers.

Put several sheets of tissue paper (kitchen or toilet, not the coloured craft sort) flat in the bottom of a plastic tray. The trays and boxes that things like mushrooms come pre-packaged in are good for this. Pour a small amount of water on the tissue until it is damp, but not waterlogged. Sprinkle some cress (or mustard) seeds evenly over the tissue. Put the tray in a sunny spot such as a windowsill and within a few days the seeds should have started to sprout.

When the cress is 1-2 inches it can be harvested with scissors. Snip off as much as you want. Very nice in cheese or egg sandwiches, or salads. Remember to plant more to keep a constant supply going.
You can also grow 'funny hair' by using half an egg-shell(cleaned first) with a small bit of tissue in it. Sowing a few seeds in this will produce an egg with a mohican hairstyle!