Tristan Louis has produced a round up of the main offerings from the major players, putting the Google Video Store in context. It's not complete, of course -- it doesn't include the Sony DRM, for example, or independent offerings such as Starz and its new Vongo service. And it does include AOL, which is only a major portal for the (shrinking) number of AOL users.
Mqanwhile Gary Price at Search Engine Watch has a round-up of the online video services already available in the US.