Space.com is carrying this nifty article about "Iridium flares". Seems the satellites that make up the Iridium communications system have a quirk in their design that can briefly turn their solar arrays into mirrors, causing them to shine several times brighter than Venus for very brief moments. To spot one on purpose, you have to know exactly where you are and what time zone you're in. The article links to several sites that can take that information and predict when you'll be able to see the next flare.