Do you have a whole collection of unwanted CDs or DVDs gathering dust around the house? Recycle a big collection into a functional dumbbell. Buy a 12-inch threaded rod from the hardware store and four nuts that will fit snug on the rod. Attach two nuts on each end of the rod and twist until they are about 3 inches in. Thread 25 CDs on each side of the rod and then secure with another nut. Use the 5-pound dumbbell when doing crunches; it's soft enough to rest on your stomach during a sit-up to add just enough resistance to your workout routine.