When you find a nice legal mp3 song on the internet, you can just turn it into a Ringtone with RingtoneMaker MP3.
Just select the song, select and cut the section of 40 seconds from the song that will play as a ringtone on your iPhone.
The app will crawl the entire website for all the songs available, and show you a list for selection.
You can also save your favorites sites for later crawling.
You can select the depth of the crawling, RingtoneMaker will make the hard work of searching.
You can also select a song from your iPod and turn it into a nice ringtone in your iPhone.