Clipomatic is a clipboard cache program - it remembers what was copied to the clipboard even after new data is copied, and allows you to retrieve the old data. While there are many programs that do the same, none are quite so convenient, simple to use, or efficient as Clipomatic.
Using Clipomatic is simple. All you have to do is start it up, and it will start monitoring the clipboard and recording its changes. When you want to paste an old item, you just put the keyboard cursor where you would like to paste and press Ctrl-Alt-V instead of Ctrl-V. A menu pops up with your clips - you can select one with the mouse or with a single keystroke. The menu then disappears, and the item is pasted with no further work on your part.