Whitney passed along an interesting find, which I was about to balk at ("bah! Masking tape and a Sharpie is good enough for me!"), but then I took another look and thought it might actually be useful in some situations:
A co-worker just turned me on to this product, Timestrips. It’s a tag you place on items in your fridge that lets you know how long the item has been there. Seems like a great thing for jarred baby food that should only be open in the fridge for a few days.