Mac OS X: There are several clipboard history and management tools for Mac OS X, but most of them cost money and provide so many features that they're actually a little difficult to use. Clipboard History simply remembers your clipboard activity and makes it easily accessible from pretty much anywhere.
In terms of clipboard management, all Clipboard History does is keep track of everything copied to your clipboard for a specified amount of time (the default is 50 items, but you can set it to more or less). It's simple and to the point. What's great is if you want to access your clipboard history, you can do so in a variety of ways. Clipboard History can live in your OS X menubar, dock, or both, and each location provides access to your your clipboard activity. The 10 most recent items are assigned hot keys as well, so you can press Command + 1, Command + 2, etc., to easily access past items. If you can't remember a past item's location, you can set a specific hot key to bring up the Clipboard History menu at mouse point. Basically, you can get at Clipboard History from pretty much anywhere. The only thing it's missing is accessibility through a right click.
Clipboard History is available right now, for free, on the Mac App Store.