There's so much out there on the crap websites that I find it impossible to sort through thousands of tracks to find ONE useable or good one.
Try ibaudio.com. Great selection, quality tracks, reasonable prices. One of the biggest headaches about music licensing is just sorting through the mountain of content that's out there. Most of the bigger libraries have people on staff just to help you find tracks that are appropriate (for a hefty fee, of course). The bigger the library, the more garbage to weed through to find anything of quality.
Once you find a few composers or sources that work for you, you'll have a much easier time of this. Eventually you build up a list of resources for different needs. If I need something high-intensity or heavy I go to X, if I need an upbeat bed for a corporate video I go to Y, etc.