Harmonix has already stated that the entire "Abbey Road" album will be released as downloadable content for "The Beatles: Rock Band" sometime after the game hits on September 9th. Apparently that's only the beginning.
An article in The New York Times today states that "Sgt. Pepper's Lonely Hearts Club Band" and "Rubber Soul" will also be coming as full albums for DLC sometime after launch. No dates are mentioned, but I'd guess they're going to roll each of them out over the course of several months.
In case you're wondering, there are songs from the above albums in the boxed version of the game. The DLC albums will basically include all the other songs that aren't on the boxed version of "The Beatles: Rock Band," basically filling in the blanks for hardcore fans.