Watch the The I-IV-I-V online guitar lesson by Ravi from Guitar Lab: 30 Rock & Pop Progressions
Another way to expand upon the I-IV-V is to return to the I chord in between. This extends the more common I-IV-V and gives it less of a blues feel and more of a folk or pop style. Try playing the rock G (using your third and fourth fingers) instead of the more traditional folk G. Depending on the song you play, this can make the chord changes easier. This will add another dimension whenever you come across the G chord, so experiment with both and decide for yourself which one sounds better in a particular song.
Examples: Brown Eyed Girl, Teach Your Children, On Top of Old Smokey, You Shook Me All Night Long, American Pie, Free Fallin'