A lot of software and educational websites charge for their services.  The costs can quickly add up if you are not careful, and you might find yourself paying for inferior products.  Here is a list of quality products that I believe are worth the investment.

Soundzabound - http://www.soundzabound.com/  
Soundzabound is the answer to educators’ prayers. Students always want to add music and sounds to enhance their assignments, and as educators we want to encourage creativity, but also teach students to respect intellectual property. Soundzabound solves this dilemma as it is still the ONLY ROYALTY FREE MUSIC Library who understands the growing technology requirements and licensing needs for education, having been created by educators for education. Visit their website today to find the licensing package that best suits you.

BrainPop & BrainPop Jr. - http://www.brainpop.com/
BrainPOP and BrainPop.Jr have short animated movies and quizzes on various subjects. Try a free trial or purchase the subscription that suits you.