One of the best things to do (because, let's be honest, you're probably not the composer from one of the epic nintendo classics) is to look up classical pieces whose copyright has expired and 'chip' em.  I highly recommend Bach.

http://www.youtube.com/watch?v=_4IRMYuE1hI

Some parts might be useful, remix, try it backwards, (Hmm... someone should totally code a chiptune inverter... probably me... I'll do it after the next procrastinators convention.)

Bethoven's 5th, 2nd, pentambic scale, 

Bach: Trio Sonata,\

Bethoven romance for violin and orchestra Op 40

Mozart Violen Concerto no 5

Prokofiev Violin Concerto no 1 in D major, 3rd movement  (Still copyrighted, need to check)

(Let me know if any of them are still copyrighted.

Statistically, the odds of the one who makes the chiptunes being the greatest composer who ever lived... 

http://www.youtube.com/watch?v=V92OBNsQgxU As seen on bugs bunny. n.n

Though the number one epic audio moment is when I realized Star Ocean had spoken audio, FTW!!

Additionally, look up Sea Chanty's as they might provide interesting world/action music... if 'pepped up' a bit.