[Disclaimer: I have no relationship to any of the following vendors.]
PartnersInRhyme — http://www.partnersinrhyme.com/ — Has one of the best sets of terms for using their music available. They offer music of every kind, sound effects, nature sounds, and video loops. They have a number of free selections of music, sounds and video. Their prices are excellent for the amount of content they provide and its quality. The only problem you might have with them is that you have to buy an entire “cd.” You can’t just find one track and download it. (You can download the “cd” or “collection” or “library.”) But most of the time, you’ll be using the same genres of music over and over in your videos, so a collection of the same kinds of music is a good idea. And considering the number of companies that charge $30 for just one track, buying a “cd” with about 19 tracks for $90, for example, makes the music very inexpensive.
Rumblefish –http://www.rumblefish.com/index.php –licenses music to go with videos and is a YouTube partner. Works with all video sites. Licenses for personal and commercial. Very inexpensive for non-commercial uses. Moderately priced for commercials uses. Has a function that allows you to upload your video and sync your music selections to it to try it out before you buy it. Very useful.
NEO Sounds — http://www.neosounds.com/#!/?mod=default — Moderately priced. Easy to browse and search. You can browse by music genre, production genre, moods/emotions and instrumentation. You can buy a whole collection or a 30-second loop. Good previews.
Stock Music Boutique — http://stockmusicboutique.com/ — much more limited selection than others on the list, but very high quality. The license is generous and the cost is moderate compared to most. Some free selections and they are as high quality as paid-for. Easy to use and understand site and terms.
StockMusic.com — http://www.stockmusic.com/ — Well-known site. Easy to browse and search. Has music, sound effects, and production elements. Average pricing. Previews available.
iStockPhoto — http://www.istockphoto.com/audio — iStockPhoto is great for people who want one-stop shopping since it has photos, illustrations, video clips, audio (music and sound effects) and Flash animation. Again, average pricing for stock. I find it annoying that you have to join and buy “credits” rather than dealing with real money. Terms are average (which means not nearly as good as PartnersInRhyme.)
Audiomicro.com — http://www.audiomicro.com/ — Easy to navigate and understand. Good music. Large selection. Average terms and pricing.
Premium Beat — http://www.premiumbeat.com/ — excellent music, reasonable license terms, moderate pricing.
All Stock Music — http://www.allstockmusic.com/ — works on the membership with credits type plan. Not very expensive and has a pretty good stock of music.
Music Bakery — http://musicbakery.com — average pricing — maybe a little more expensive than others on this list that I’ve called “average” but only by a few dollars. Good selection and easy to use and understand site.
RoyaltyFreeMusic.com — http://royaltyfreemusic.com — one of the better-known sites. More $$ than I want to pay, but has top-notch music. Terms are about average.
So, go forth and shop for music. If you have any suggestions for other links, contact me through my contact box on this page or sign in and comment.