In the English speaking world, YouTube is by far the most popular video sharing site. Despite its huge size, and being regarded as the go-to site for finding videos, there is a lot of user-uploaded video content available on other video sharing sites.
Vimeo and Dailymotion, two common alternatives to YouTube
Vimeo was launched in November 2004, making it a n older video sharing site than YouTube (Youtube was launched in February 2005). Vimeo also had HD video capabilities before YouTube did. Vimeo is often used for more professional looking videos such as short films, independent music videos, and mini-documentaries (especially for embedding in websites).
Dailymotion was released about a month after YouTube. It was developed in France, and is popular in the French speaking world.
Foreign language video sharing sites
There are some very popular foreign language video sharing sites that are almost unheard of by the English speaking monolinguals.
Chinese: Youku, ku6.com, 56.com, Tudou
Japanese: Nico Nico Douga (registration required for watching videos).
German: MyVideo
French: Wat.tv
List of video sharing sites
On L-Lists, there is quite possibly the most comprehensive list of video sharing sites on the internet, with over 120 sites listed:
Hard To Find Videos 