As well as copyrighting your song, you should also join a PRO (Performing Rights Organization.) These organizations, within North America, include ASCAP, BMI, and SESAC. SESAC unfortunately is reserved for those whom are already making a strong impact in the songwriting world. However, ASCAP and BMI will take anyone whom has recorded works. You want to register as a writer and publisher. This assures that in the event one of your songs gets played on the radio, on TV, or anywhere for that matter; you are taken care of in getting royalties. Even if you don't aspire for that, it is something that looks very professional and it helps you get a grip on that end of the music business. Here is my ASCAP information:

Writer Name: Douglas Showalter
Publishing Name: The General Public (ASCAP)

Here are links to where you can sign up for ASCAP or BMI. Again, this is one more step in helping you cover up all the business aspects of your original work;

http://www.ascap.com/about/howjoin.asp

https://applications.bmi.com/affiliation/joinen.aspx?link=navbar

Again, you need to join as both a writer and publisher to be on the safe side.