I currently have seed and bean sprouts growing in jars and small sprouting trays, a shiitake mushroom log started, and a batch of future salad greens in small containers (not seen in photo).The little gardens are "watered" every 12 hours or more. I talk to the sprouts while I am puttering around in the kitchen, which is not much different from my gardening outside in the summer!
The following is a breakdown of the three types of little gardens I am tending throughout the winter.
Sprout Gardens: beans, seeds, grains, and nuts
Nutrition: Sprouts are one of the most highly concentrated sources of vitamins, minerals, enzymes, and proteins that can be consumed. In a matter of a few days, some sprouts can grow to 15 times their initial seed weight, and B vitamins increase up to 1200%. 
Cost: The small spoonfuls of seeds, beans, grains, or nuts to be sprouted will cost pennies, and will equal cupfuls of delicious vegetables. I harvested two cups of alfalfa sprouts after starting with less than 1-1/2 tablespoons of tiny seeds.
Requirements: Sprouts can be grown in canning jars with cheesecloth and a rubber band as a strainer lid, special sprout bags, and stackable trays of various designs. Soil and direct sunlight are not needed, and room temperature is sufficient for successful sprouting. You will need water and a sink to rinse the sprouts every 12 hours and more often if conditions are warm and dry.
Fungi Garden: mushroom logs
I have wanted to try my luck with a mushroom patch for a while and was excited to receive a shiitake log as a gift from a good friend and garden buddy. The log sits under a humidity tent which appears as a fuzzy white and brown blob to the rear in the article thumbnail photo. The picture at right is what I hope mine will look like before long (curtsey of DG's critterologist).
Nutrition: Mushrooms are a fungus, and in general are very nutritious, contain 20% protein, are high in trace minerals like copper, and thought to help reduce the risk of cancers with their antioxidant components. Shiitake and reishi mushrooms specifically have been used as medicinal mushrooms because of their immune-boosting, infection-fighting, and anti-tumor properties.
Cost: I am not sure how economical a mushroom log is! You could consider the value of watching the fungi grow and knowing how it was cared for. Depending on how prolific your log is, you may indeed come out ahead financially if grocery store prices continue to rise.
Requirements: This mushroom patch required temperatures between 60-80 degrees; indirect natural light, and to be misted with water (spring, well, rain, or boiled and cooled tap water) a few times per day.
Salad Gardens: leafy greensNutrition & Cost: Salad greens are the sprouted seeds, grains, or beans allowed to mature for a few more days and sometimes grown in a shallow tray of soil. They are much less expensive than traditional lettuce (Iceberg, Romaine, etc.) and much more nutritious and flavorful! They contain as much vitamins, minerals, enzymes, and proteins as the sprouts, but now include chlorophyll. 
Requirements: Shallow trays of soil 1" deep, plenty of indirect sunlight; and water are the only requirements for these greens. There are now small, tightly woven baskets made especially for the purpose of growing greens without soil. The greens are pulled out roots and all, or cut at soil level when harvested.
So what are you waiting for?
Weight loss diets utilize sprouts, mushrooms, and greens because they are low (or no) fat or cholesterol, low calorie, high in fiber, and easily digestible. Medicinally, they are used for their great nutritional and healing values. They are tasty, easy to grow, inexpensive, ready to eat in a short time, and do not take up much space. You could have a few tiny kitchen gardens ready in less than a week if you start right now! Have fun!
 Steve Meyerowitz. Sproutman's Kitchen Garden Cookbook. 5th ed. Book Publishing, TN. 1999.
 Fungi Perfecti. The Shiitake Mushroom Patch. http://www.fungi.com
 Ann Wigmore. The Sprouting Book. Avery. 1986.
Special thanks to critterologist for her shiitake mushroom log photo (beautiful)!
Thank you Michael for the containers to make the little Salad Greens gardens!