Ringtones, baby! THREE applications make the Treo sing.
Electric Pocket has released Ringo, a ring tones application for the Handspring Treo communicator. Users can take any Palm OS alarm tune and convert it into a Treo ringtone. Users of Ringo (which I can't help but pronounce with a British accent) can also use an on-screen piano keyboard to compose their own tunes.
Those less musically inclined can buy ring tones from TreoRingTones.
Another ringtone editor for the Treo is Monkey Editor from MonkeyEditor from Primate Systems. You can also purchase ringtones from the company.
Last of all, for $5.95, Proxyminds offers iRing.
Now if I could only get the James Bond theme for my Treo (hint, hint). Ringo is now available for free if you use the SMS registration (which should be pretty much everyone) or for $9.95 if you don't want to use that method for some reason. I like the concept of SMS registration and hope that other software vendors take this up in the future.