Agree with this, it's a great resource I use at work. It really is an awesome program that lets you greatly customize the feel of the music. The tracks may seem expensive at first but you can generate MANY variations from the same track. Just be aware this does not apply to the older tracks in their library.
There's also a company called Footage Firm that sells stock footage and music and they are always have giveaways where you pay only S&H for the discs. It's not as good as SmartSound but you can't argue with the price! They also time their tracks for broadcast, so they will typically have 30, 45, 60 second versions apart from the full track.
There is also an affliated site called Videoblocks.com that is subscription based and they offer a 7-day trial to check it out.