MP3: This is an MP3 sample of duty-free videogame battle music. MP3 is easy to encode and decode and it is very widely supported.
OGG: Another sample of videogame music, this is called "Deeper". It's in OGG format. The OGG container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata.
It's often better quality than MP3.
WAV: This is beach sounds in WAV format. WAV is supported by HTML5, but isn't as popular as MP3.
MP4: This is a beautiful video of a beach in MP4 format. MP4 is able to encode mixed media data (video, audio and speech).
OGG: This is a nice video of a dying fire in OGG format. Theora is a video codec developed by Xiph.Org Foundation, and it's one of the 3 video formats supported by HTML 5.
WEBM: These are beautiful foggy mountains, viewed in Webm video format. Webm is an open media file format developed as a royalty-free alternative to use in HTML5.