Dot-It Light

It's small, round, sticky, provides light, and is useful in many everyday situations. No, it's not a radioactive spitball, it's the Dot-It Light, an inexpensive adhesive light that uses LEDs (so it lasts for a very long time) and sticks to any surface without leaving marks when you remove it. Just stick it somewhere and give it a tap, and voilá, you've got some nice illumination. When you want to move it, just pull it off and the adhesive will still be good. $9.49 USD.