New 21.5-inch Retina 4K models expected.
iTunes Music Store Selling Videos Now
This feature is demonstrated in the Feel Good Inc single (iTunes Link) which was used in the most recent iPod Ad (Rollerskating).
The videos for this particular artist are provided with the album purchase only and are not available for individual purchase. Purchasing the album provides you with 4 short .mp4 videos. These particular videos are 480x272 pixels, 30FPS with 44kHz audio.
These videos are simply animated shorts rather than music videos - and in this particular instance - do not utilize any Digital Rights Management.
Update: Other videos included with an album:
The Antidote by Morcheeba ($9.90 for 10 songs, 1 video)
Warning Shots by Thievery Corporation ($1.98 for 1 song and 1 video which is 27MB, 480x360).Stand Up by Dave Matthews Band ($11.99 for 14 songs, 1 video, 1 PDF)
Pink Bullets by The Shins
($1.98 for 1 song, 1 video)
At this point, videos appear to be "extras" to provide incentives for customers to purchase full albums. Apple does not appear to be selling videos individually at this time. Similarly, Apple offers PDF Booklets for some other album purchases (ex: In Between Dreams by Jack Johnson).
Of interest, the Warning Shots' Video adds a $.99 premium to get both the song and video ($1.98 total). Meanwhile, the Warning Shots song is available by itself for $.99.