Here are a bunch of songs that always get me in a good mood:
Train - I'm About To Come Alive
Vienna Teng - Harbor
Sarah McLachlan - Hold On
Turin Brakes - Red Moon
Peter Gabriel - Red Rain
<shameless plug>
Whenever I can't find the right kind of motivational music, I'll just write it myself:
Jim Offerman Band - This Is Me
Jim Offerman Band - Hold On To Your Dreams
The first one helped me overcome my low self-esteem and the second one kept me sane while my entire world came crashing down around me. You can check them out
here, if you like.
</shameless plug>
cheers,
Jim.