There are many sound effects and music resources online. While most of the resources listed here are free to download, always check the copyright status of any works before using them in your project.
Via the SVA Library:
Westar Music allows you to download over 300,000 tracks of Production Music, Production Elements and Sound Ideas sound effects in your choice of mp3 and Broadcast WAV files. All new releases are immediately posted on the site and we release thousands of new tracks every year.
Sound Ideas offers sound effects and production elements for television, film sound design, game development, post-production, interactive media and any other professional or educational audio production use you can imagine.
On the open web:
The BBC Sound Effects Archive is available for personal, educational or research purposes. There are over 33,000 clips from across the world from the past 100 years. These include clips made by the BBC Radiophonic workshop, recordings from the Blitz in London, special effects made for BBC TV and Radio productions, as well as 15,000 recordings from the Natural History Unit archive. You can explore sounds from every continent - from the college bells ringing in Oxford to a Patagonian waterfall - or listen to a submarine klaxon or the sound of a 1969 Ford Cortina door slamming shut.
Public and commercial studios in NYC: