CNET reports that independent developer Zac White has released an open-source framework for iPhone developers called OpenClip, which in theory enables copy and paste among any programs that support White's standard.
Currently, there are no such applications, but CNET claims that American Heritage Dictionary and Roget's Thesaurus, Twitter client Twittelator, notepad application MagicPad, finance lexicon Wall Street Worlds, and others will be adding support in the near future.
Perhaps most interestingly, CNET's article claims that Apple has officially stated that it will eventually add a clipboard to the iPhone OS.
You can visit OpenClip's official site here. (The link provided in the CNET article appears to be incorrect.)
Editorial: This is exactly what I feared would happen if Apple continued to delay adding a clipboard to the iPhone OS. I think Zac White has a great idea and great intentions, but the possibility of iPhone apps having multiple competing clipboard standards could easily become a nightmare, especially since Apple's own apps will presumably never support any clipboard standard other than Apple's (if they ever release one). Apple needs to put an end to this by getting a clipboard built into the OS.