I also have to agree that "Bring Down The Sky" is well worth getting for Mass Effect 1. In fact, there's an amusing counterpoint to the situation from BDTS that comes up in Mass Effect 2 with one of the DLC episodes.
Mass Effect 2 really needs a new purchase because the Cerberus Network DLC gives you an in-game NPC, additional weapons and a few additional missions. One highly recommended to get new and also well worth getting all the DLC along with it. Especially "Kasumi's Stolen Memory", which gets you another NPC and a very useful weapon upgrade, as well as "Lair Of The Shadow Broker", which gets you a new biotic power, some additional items and a very useful ability to re-spec your teammates. LoTSB is also a fantastic piece of DLC on its own from a story perspective.