According to user "De-Mon", Sony and EA are on the verge of announcing some kind of Mass Effect port entitled Mass Effect: Genesis. "De-Mon" anticipates that the title will be announced during either of the companies' GamesCom conferences tomorrow, but suggests a magazine reveal over the next three weeks is also possible.
The assumption is that the game will feature at least Mass Effect 2, though given the narrative focus of the franchise we suspect that it'd have to include a recap of the original game too.
We'll find out for sure tomorrow. File this one firmly under rumour for now. This could be huge if true though; Mass Effect is one of the XBOX 360's biggest franchises.