The BOSU is a balance training toy that can be in many different ways, on either side. BOSU actually means Both Sides Utilized.
I've used the BOSU at the gym, and it's a really fun way to build core strength. We do sit ups and other contortions on it in pilates class. I love the thing--it mixes exercise up and keeps it interesting.
I wouldn't buy one for home--it's too expensive at $150. But I do like my very inexpensive balance ball. Mine was $10 at target, or you can spring for The Biggest Loser Core Advantage Stability Ball for $25.
Did you see Fitz surfing on her BOSU to build core strength, above?
What is one piece of workout equipment that you like? Do you buy special toys like this one or do you make do with what you have at home? For example, a chair and staircase are great for many exercises.