Guitar Hero DLC (today) - Lady Gaga - Just Dance - Maroon 5 - This Love - Owl City - Fireflies
DJ Hero DLC (today) - Lady Gaga's "Poker Face" mixed with "Girls On Film" by Duran Duran - Pussycat Dolls' "Buttons" beat juggle - Rihanna's "S.O.S." beat juggle
Also, according to RockBandAide...
You better go get some Microsoft Points, because you don’t want to miss Liveapalooza on Xbox Live from July 6th to July 12th. What is that, you say? According to a post over at IGN, it looks as though music game add-ons such as albums, track packs, and songs for Rock Band, Guitar Hero, Band Hero, and Lips will be put on sale! No word yet on what albums, packs, and songs will be discounted, but as soon as I find out, I’ll post details here!
Not to thread hijack, but has Raiden II been released on XBLA? As far as I remember it's pretty unplayable via emulation because of the way the arcade game was programmed/built, and there has never been a port of it to any system.