protecting your song: 

You should register all of your material with the Copyright Office in Washington D.C.  The form you will need is FORM SR (sound recording); you will also have to send them a non-returnable copy of the song and a $65 fee. ($65 is the fee for paper filing; Internet fee (see below) is only $35)

saving money by protecting a collection of songs

If you write a few songs every month this can get very expensive; but there is a way to cut costs by copyrighting a collection of songs. For this you will need FORM PA  (performing arts) to register the collection and keep a copy on one tape.

Then you will need FORM CA (supplemental registration for Correction/Amplification) by filling in the "Amplified Information" area with each separate song title. This way you can copyright a whole body of songs for one low price.

for more information write:

Library of Congress Copyright Office 101 Independence Avenue S.E. Washington, D.C. 20559-6000

copyright via the internet

Now, thanks to the internet  eCO ONLINE filing is available and the advantages are numerous.  The filing fee is lower ($35)the processing time is much faster, there is on-line status tracking, uploading mp3 files directly,  and it is available 24 hours a day.  It doesn't make sense to deal with the copyright office in Washing DC any other way.

For more information:  www.copyright.gov

protecting your songs by other methods. 

I've heard of various ways over the years: such as sending your songs to yourself via registered mail and not opening the envelope until you need to prove ownership.  (the date of registration is your protection). I don't know if this method has ever been recognized by a court of law.

Copyrighting a song over the internet via the U.S. Copyright Office (especially an album of songs at the same time) is very reasonable.  Why take the chance on any other method. The safest way to protect your creative effort is through the copyright office in Washington DC.