Default tunes & tones for most phone do not really appeal, and changing your ringtone on the Nexus One is relatively simple, here are the steps:

1. Plug in your phone to your computer via your USB & mount it.
2. On your SD Card, create a folder called ‘Media’
3. Within the ‘Media’ folder, create 3 sub-folders called, ‘Alarms’, ‘Notifications‘ & ‘Ringtones’
4. Copy your ringtones or tunes into the relevant folder that you want to use them for.

If you already have the song playing on the phone, and want to use it as your ringtone, here’s how to set it up:

1. Open the Music application
2. Select the song you want to use as your ringtone
3. Goto Settings > Use as ringtone

The song in your playlist will now be automatically set as your default ringtone.