Below is a sample WebM video encoded with Wildform Flix which is a FREE WebM encoder. You need a HTML5 enabled browser and browsers that support WebM videos.
And while at it, why not read WebM Overview.
Which browser can see this video?
I tested playback with these Chromium builds (Chromium is the base of Google Chrome browser, note that these Chromium builds are daily builds should be considered preview releases):
The Red Cliff trailer is (C) 2009 Magnolia Pictures.
View another Example WebM Video (larger dimensions)