I'm a little behind, so here is the influx of new Xbox Live Marketplace content that hit on 6/12. Thanks to Major Nelson for the update.

++++++++
Today on Marketplace (6/12)
Instead of a post for each item (and since its only a few themes and picture packs) I decided to roll everything up into one post for what is new on Marketplace as of now.
Unless otherwise noted, this is premium content available in all regions:

Themes
Monster Madness Character Theme
Anime Presented By Xbox 360 Samurai 7 Theme Pack *US only*
Anime Presented By Xbox 360 Gankutsuou Theme Pack *US only*
Anime Presented By Xbox 360 Gun Slinger Girl Theme Pack *US only*
Anime Presented By Xbox 360 Trinity Blood Theme Pack *US only*

Picture Pack
THE IDOLMASTER Cute Gamer Picture Pack
Anime Presented By Xbox 360 Trinity Blood Picture Pack *US only*
Anime Presented By Xbox 360 Samurai 7 Picture Pack *US only*
Anime Presented By Xbox 360 Gankutsuou Gamer Picture Pack *US only*
Anime Presented By Xbox 360 Gun Slinger Girl Picture Pack *US only*

Trailer
Monster Madness Comic Book Style Trailer *Free*