Royalty Free Music - Resources for people who need music for their games and animation.

Sound Editors - generally used for the manipulation of single mono or stereo sound files, application of sound effects, and exporting in various formats and qualities.

Studios, Sequencers and Composers - multitrack programs which allow you to combine several different sound files or audio sequences to create songs.

Software Synthesizers - keyboard/synthesizers for the computer. Virtual sound generators, usually including a bunch of sound manipulating tools and effects.

Sound Converters - Programs that allow the conversion of sound files from one format (eg wav) to another (eg mp3). Most Sound Editors are capable of outputting various formats, so if you have a decent sound editor you're probably set.

BBC Sound Effects Library - Free for non-commercial use, with credit. Paid licenses available for commercial use.

Free Sound Effects (Royalty-Free) - 99Sounds

Also see Denvish's list of Audio Tutorials!

Community Sample Packs

FIREWORKS - A Sample Pack and Drum Kit, organized by FelixZophar.

Stuck At Home Sample Pack - A Collection of samples created by the community during the COVID quarantine! Organized by Curruff.

SONNISS Game Audio GDC Archive - Each year SONNISS gives away free sound effects in honor of the Game Developer's Conference. This is their archive.