Now that Apple is offering Music Videos, Short Films and TV shows for download on their iTunes Music Store, the transition to selling full length movies is not a technical issue, but more of a marketing / licensing issue.
It appears Apple is now offering the first full-length movie for sale on the iTunes Music Store.
High School Musical (iTunes Link) is a 1 hour 39 minute Disney Channel original TV movie that is available on iTunes. The movie is 487MB and costs $1.99 - the same as all other videos on the iTunes Music Store.
This movie, however, does not appear to be linked from the main iTunes Store.
Apple has been rumored to be working on a distribution deal with the major movie studios, and is expected to launch a full-movie service alongside a Video iPod in the coming weeks.
Update: The movie is no longer available.
Update 2: The movie is back up but now is priced at $9.99. The previous pricing appears to have been a mistake. More details posted here.