I came onto the scene too late to have nostalgia for MNOG. The only lego.com flash game I really miss was a Lego Racers game called something like "Drome Racers Challenge". It was a multiplayer game so nowhere has an archive of it :(
I remember it had teams kinda like that one Steam Summer Sale, and one of the teams was called "The Exo Force" as a teaser for the upcoming Exo Force line (which, by the way, was awesome and shouldn't have been canceled).