The first things I stored were actually homemade baby food. Not only were the jars convenient storage containers, they also helped me get a better idea of how much David was eating when I wasn't feeding him store bought baby food. Since David is a skinny little fellow, the doctor often asks me detailed questions about how much he eats and having the baby food in little jars helps me answer those questions more precisely.
I also have started storing a lot of craft things in the jars. From homemade finger paint to beads, the jars are the perfect size and they close tightly. Along the same vein, screws and nails also fit well in these jars and my husband wants to store some electronic parts in them using the good old fashioned method of attaching the lids to a board with screws. That way you can screw the jar off the board but when you screw the lid on it will stay put.
Many people make spice jars out of baby food jars, often attaching a magnet to the lid so they stick to the fridge. I have not done this yet, but it isn't a bad idea. In fact, back when I worked as a night stocker (as opposed to a night stalker) at an import store a few summers ago, I remember stocking "spice jars" that looked almost exactly like a baby food jar. The downside to this is that you wouldn't have the tops with holes for controlled shaking out. The upside is that you can buy your spices in bulk and put them in the jars, which is often cheaper in the long run.
Baby food jars also make good snack containers. David likes to try to eat plastic bags when he sees me pull out snacks in them (I don't let him have them, but that doesn't stop him from trying). I feel okay letting him play with the closed jar a bit and then I avoid the squealing he makes when I don't let him have something he wants; it is quite high pitched and demanding. Also, he tends to try to climb me using whatever handholds and footholds possible to get to the item, which can hurt.
All in all, as I said not the most exciting use, but by far the one I use most often. For instance, I only need tea candle holders once every so often but storage containers I use daily.