An exercise ball is a great, and truly inexpensive addition to a home gym. For years I had to house my gym equipment in closets, and pull everything out each time I wanted to exercise. I am very fortunate to actually have a space completely dedicated to exercise now, but many of the materials I used before the room, I use in the room.
Of these the exercise ball remains a constant. For a long time now patients have been given these as a tool during rehabilitation, and now fitness experts have come to recognize their effectiveness. These balls are great for improving balance, and core strength and as such are not fad items.
There are what appears to be limitless exercise dvds that make use of these balls, and plenty of books that show exercises you can complete with the ball. Some even recommend using it in place of a weights bench if you are only lifting minimal amounts.
But as is the case with most things, all of these balls are not the same, and you should be educated on what to look for prior to buying. You can identify the proper ball for you by sitting on it while it is inflated. Once you are seated look to see if your hips are level with, or slightly above the height of your knees. If so, then it is for you.