Pachelbell's Canon in D Major
Dmaj - Amaj - Bmin - F#min - Gmaj - Dmaj - Gmaj - AmajGreen Day's Basketcase
Emaj - Bmaj - C#min - G#min - Amaj - Emaj - Bmaj - Bmaj
At first, you might think these two tunes couldn't be more different, right? The chords looks totally different. If you analyze each tune numerically, though, it paints a different picture. Here are the numerical progressions for each, Canon in D major being in the key of D major, and Basketcase being in the key of E major:
Canon in D Major
I - V - vi - iii - IV - I - IV - V
I - V - vi - iii - IV - I - V - V
The two songs are almost identical. Yet, they obviously don't sound anything alike. This is a great example of how different a chord progression can sound, when you alter the way in which it is played. I suggest doing what Green Day may, or may not have done here; try taking the chord progresssion to the verse, or the chorus of a song you like, fiddle with a couple of the chords, change the key, change the "feel" of the tune, and write a new melody with different lyrics, and see if you can't come up with a completely new song.
With this article, we've just started to scratch the surface of analyzing the art of songwriting. For further study, you might want to read writing songs in minor keys.