For example, I know of one -- if you bring Legion on Tali's loyalty mission in ME2, Admiral Raan recognizes it in ME3 and has different dialogue than if she's seeing it for the first time. Anything else like that?
Liara's reaction to Jack at Grissom Academy is slightly different if you had Jack as a squadmate during Lair of the Shadow Broker. Instead of saying that she'd heard about Jack's anger, she'll say that she'd forgotten how angry Jack was. The rest is unchanged, though. Terminator-HIX (talk)
I saw in a vid on YouTube that if you bring Garrus along to take the Normandy back from the clone (Citadel DLC), Shepard will recall what Garrus once said about his favorite places to fight (antic shops, but only if they are classy). Although, I don't know if you need Garrus to have accompanied you during Mordin's loyalty mission back in ME2 (that's when he speaks about that). Will-O-Wisp (talk)