I purchased SonicFire Pro. You can make the soundtracks exactly the length you want, with a proper ending too, BUT, going much longer than the song makes it sound somewhat tediously repetitive.
Here are some suggestions, and please, by all means, add your music sources and what you think of them, costs, etc.
Audio Network
Davenport Music
Digital Juice
GMP Music
Jamendo
MagnaTune
Music Bakery
Royalty Free Music
SonicFire Pro
Sounddogs
Stock 20
As you all chime in any good tips you have I will edit the above list and add the referred source in alphabetical order.