Chris Walsh and co. are getting very close to releasing the very first side-loaded homebrew app for Windows Phone 7: ringtone loader.
That should come to many as a worthy installation, even if the rumored update from Microsoft will contain such functionality. Not much is known at this time about what it can/can't do, but we imagine creating ringtones from your Zune library will be the cornerstone.
Of course you'll need to use ChevronWP7 to unlock your device first. Yeah, Microsoft would prefer you not to (shocking) but you're adults, we'll leave the ethical issues up to you.