Go to one of the song identifying sites on the Internet. Sites like Midomi.com work off your voice. Sing, hum or speak what you know and the site does its best to recognize what you're saying/singing and find a match in its extensive database. Of course, you need a microphone on your computer to take advantage of this kind of site.
Use your PDA if you have one and download a song finding application. As of 2010, numerous applications existed for smart phones, including Shazaam and SoundHound. Just like the song identifying websites, you can sing or hum what you know into your phone. The mobile versions are also good for figuring out what song you're hearing wherever you are. So, if you hear the song and can't decipher the lyrics or song title, get the PDA as close as possible to the speakers and let SoundHound or Shazaam help you out.
Visit a lyrics database such as FIndmeatune.com, eLyrics.com or Lyrster.com which can match your known lyrics without requiring you to perform in any way. This can be especially helpful if you don't have a microphone enabled computer. Of course, the disadvantage is that you have to be sure about your couple of words because the site can't pick up the music -- just the words.
Go to a site that specializes in movie lyrics if you know the song is from a film. A few can take a short lyrical phrase and run it against movie soundtracks. Some, like stIyrics.com, have the lyrics to entire soundtracks, but it's only helpful if you're sure the song you're thinking about it from a certain movie.