The Codex lists several core-supported oEmbed sites (including a few being added in 3.5):
- YouTube (only public videos and playlists – “unlisted” and “private” videos will not embed)
- Vimeo (note older versions of WP have issues with https embeds, just remove the s from the https to fix)
- DailyMotion
- blip.tv
- Flickr (both videos and images)
- Viddler
- Hulu
- Qik
- evision3
- Scribd
- Photobucket
- PollDaddy
- WordPress.tv (only [http://videopress.com/ VideoPress]-type videos for the time being)
- SmugMug (WordPress 3.0+)
- FunnyOrDie.com (WordPress 3.0+)
- Twitter (WordPress 3.4+)
- Instagram (WordPress 3.5+)
- SlideShare (WordPress 3.5+)
- SoundCloud (WordPress 3.5+)