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.