When BioWare announced the Mass Effect Trilogy, one key detail was missing: would any DLC be included? Given its budget price, many were expecting the compilation to omit any downloadable add-ons, preventing it from being a truly definitive re-release. Apparently, there will be some DLC included in the box, depending on which platform you're playing on.
BioWare's official site (via Joystiq) details the differences between the various editions. The Xbox 360 version of the Trilogy will include Mass Effect 2's Cerberus Network, which unlocks the Normandy Crash Site, various weapons and armors, and DLC character Zaeed. Mass Effect 3's Online Pass is also included in the box. Essentially, everything included from the original retail releases of the three games has been replicated in this collection.
The PC version of the Trilogy will include everything the Xbox 360 version has, but also adds Bring Down the Sky and Pinnacle Station for the original game. (Bring Down the Sky was released as a free download, but the latter is still available for $5.)
Information on PS3 DLC will be "available soon," as that version of the game is coming after the PC and Xbox 360's November 6th release.