[edit] Steps

Download a free audio editing program, like Audacity.
Start Audacity and iTunes. Start playing some music in iTunes at a normal listening volume.
Select "Stereo Mix" as your source of input. Stereo Mix is any sound that comes out of your speakers. ANY SOUND! So exit any program that makes sound like IM services, Email, etc.. Near the bottom left in audacity, set the "project rate" to 44100.
Monitor the input volume in Audacity. See Audacity's help files for more info on this. Adjust the slider next to the microphone icon until the input volume stays around just over 3/4th's. This is called normalizing. The volume slider in iTunes should be at full.
Record a test clip, to ensure you have everything set correctly. The test clip, should playback at the same volume and quality as iTunes. Once everything is good, click the 'X' on the new audio track to delete it.
Press the record button in Audacity, then start playing the song in iTunes.
Listen as your music is released from its DRM prison. Once the song is over, press stop in audacity. Go to File > Export as MP3.
Pick where to save the song and give the file a name.
Click save and fill out the song information in the new window. No fields are required, but you want the keep your music organized, right? Do what you want with the original song. Your new copy can be copied indefinitely and can be treated as a regular MP3.

Another way

Open Itunes
Click edit, select preferences.
click the advanced tab
Click the first two check boxes from the top
Make a new playlist
Drag purchased songs into the playlist(can be audibooks, movies, music,ect)
Click "burn Disk" and select Audio CD, and Include CD text
Insert a CD-WR disk (if you will be burning multiple times, you can use the same cd)
click burn
rip songs back into Itunes and the DRM will be gone!

[edit] Tips

There may be an easier way to do this, so do your own research.
Learn how to use Audacity. It is a very powerful audio editing program. You can easily create your own mixes or sound effects with it.
The method described above can be used to rip songs from Internet radio stations.

Although removing the DRM protection from songs is perfectly legal, using Audacity to do this is not. But do not fear the man! In the minuscule chance you get into trouble for doing this, your consumer rights can put the jury on your side.
Copying music in this fashion can also lead to a measurable loss in sound quality. Further copies in a similar fashion will continue to degrade the quality. Remember, mp3 is a lossy algorithm. Decide for yourself how much quality is an acceptable sacrifice for being able to listen to your iTunes music elsewhere.