When looking for some lyrics I'm not sure of, I often run upon sites that have chord names or tabs with the lyrics. All too often these chords are very wrong. It's nice when people try to help by posting these, but wrong chords are not very helpful. A site that has many songs with excellent chord choices is Dr. Uke's (Dr. Jim Rosokoff) at http://www.doctoruke.com/index.html. The songs are in pdf format and are easy to print.
How does one decide if a chord is the correct one? Trust your ears. If the chord sounds wrong, it probably is. Often, a chord's notes will include the note the melody is on for at least part of the chord's duration.