For a song that makes doing even the simplest tasks seem like doing the most incredible achievements just because you're listening to the song while doing them, look no further than Jurassic Park's Main Theme. Talk about grand and epic.
For me, 'motivational' generally involves 'songs that wake me up', because they stop me from falling asleep when I need to do something. The following songs fit that pretty well...
the goo goo dolls - Big Machine (not the lyrics, just the music itself generally kicks my brain into action)
Dizzee Rascal & Florence + The Machine - You've Got the Dirtee Love (as above)
Republica - Ready To Go (title of the song = self-explanatory)
Survivor - Eyes of the Tiger (hi, Ciddies)
Europe - The Final Countdown (hi, Ciddies)
Hall & Oates - You Make Me Feel Brand New (a happy, upbeat song to both wake me up and put a smile on my face)
Frou Frou - Let Go (perhaps not a wake-up song but I like listening to music like this when I'm in a creative zone)
Example - Watch the Sun Come Up (ditto the above)
And Flobots - No Handlebars deserves a mention because the lyrics always appeal to me as a motivational thing.