I have already played through the trilogy a few times but I don't have any of the DLC you have to pay for. Since some of them are $15 a pop, it can really add up. So, which, if any, are worth my time and money? If they won't add much to the story or aren't that fun to play, I don't want to bother.
It might be cheaper to look for a copy of ME2 that has Lair of the Shadow Broker, Overlord, and Kasumi: Stolen Memories already on it.
As far as ME3 goes, Leviathan and Citadel are definitely worth the money (in my opinion). Omega is alright, I only saw the need to play it twice though.