There are lots of clipboard managers. What's nice about ClipMenu besides it's $0 price tag is its great integration with Mac OS X. Just hit the Shift+Cmd+V shortcut to get the pop-up menu with your history of your copied items or your snippets of text in whatever text box you're pasting into.
You've also got a ton of customisation options like selecting your history sort order, how many items you want to store, changing the menu bar icon, and more. You can perform actions such as pasting as file path or pasting as plain text as well.
And then there's the really useful snippets storing, where you can save frequently used pieces of text you type a lot — pieces of code or email signatures or whatever. (We like using text expansion, but this is another option if you don't feel like remembering the shortcuts.)
All in all, ClipMenu's a great little utility that could enhance your productivity.