There's a multiple clipboard option of course, but CopyPaste Pro also lets you edit the contents of a given clipboard (or "clips" as they call them) with its built-in word processor, create an archive of previous clips and even review clips via a "clip browser," which resembles Mac OS X's application switcher.
If you're one of those users who just can't live with the standard Mac OS clipboard, check out CopyPaste Pro.
CopyPaste Pro requires Mac OS X version 10.4.x or 10.5.x. For a short time, users of CopyPaste can upgrade to CopyPaste Pro for $20US. On May 12th, the price will go up to $30US.