It's easy to forget that you left something plugged in and find out the next day that you accidentally left a battery pack charging all weekend. However, by placing all of your charging devices in the middle of the room where they're easily visible is a great way to remember to unplug them when they're done charging.
We all should know by now that leaving devices and rechargeable batteries plugged in for an extended amount of time isn't healthy for the battery, but it can be difficult to keep up with that rule if you're a forgetful person. However, you can plug in a battery pack or smartphone to an extension cord and place it in the middle of the room, that way you'll never forget it's there.
Of course, it's not the prettiest solution, especially if you're a neat freak, so you could get Belkin's Conserve Socket, which shuts off power after a certain amount of time. However, if you're especially frugal, the extension cord trick works wonders.