I know that there's Cinescore, etc. to create soundtracks, but I've always felt that they're either unoriginal and lack flexibility, or you have to buy more themes or royalty-free music to expand your options. I have no vested interest in any program over another, but if you do low-budget projects like I do, here's another option: I purchased Band-In-A-Box (www.pgmusic.com), and then bought a sample library (you need one that can be a "VSTi plugin." I purchased SampleTank 2 XL from mtlc.net; it has 4.5 Gig of professional sounds. You can check out its sounds at www.mtlc.net or www.sampletank.com). BIAB will create original compositions from hundreds of different genres/sub-genres of music, and you don't need to have much musical knowledge. You can just click on the style you want, then "Create Chords & Melody" or even "Create Solo." Then you tell SampleTank which instruments you want to play each part, and it sounds like original instruments. You can also import any MIDI file you find on the instrument, change it around a bit, add a lead or new melody/chord structure, and now it's your original tune.
It's not cheap at first to buy the full BIAB program ($269 for the MegaPak) and then a good sample library (I paid $299 for SampleTank 2 XL at mtlc), but I just created a video project with a great original soundtrack exactly how I wanted it to sound, added in the costs of the programs as overhead as I came in low priced anyways, so now I have the programs for future work. This is just a different option; I've tried out the other soundtrack options, and there's just minimal flexibility once you've used their themes once or twice (and they probably sound almost just like everyone else).
It's not cheap at first to buy the full BIAB program ($269 for the MegaPak) and then a good sample library (I paid $299 for SampleTank 2 XL at mtlc), but I just created a video project with a great original soundtrack exactly how I wanted it to sound, added in the costs of the programs as overhead as I came in low priced anyways, so now I have the programs for future work. This is just a different option; I've tried out the other soundtrack options, and there's just minimal flexibility once you've used their themes once or twice (and they probably sound almost just like everyone else).