audiojungle is good for background music. A tad pricy, but not too bad considering the quality. (tim mcmorris in particular has an incredible list of upbeat tracks that work well for corporate presentations, app demos, etc. )

http://www.revostock.com/

http://audiojungle.net

http://audiojungle.net/user/timmcmorris/portfolio

One other quick tip if you are just starting out in this. Put your script together first. Have the voice over work completed until you are happy, then tweak the video templates to match the voice over work.

If you try it in reverse order it will end in frustration and a much lower quality product.