I think that most remember his "Walk On The Wild Side" as the first song they heard from Lou. (Not sure but I believe that was his first track that made regular radio play, at least in the US). That was (as I saw it, popularity-wise) followed closely by two Velvet Underground tracks, "Perfect Day" and "Pale Blue Eyes". Of course there is also "Sweet Jane" and its famous secret chord!!
Ah, he will be missed... Lou was 71 years old??!? Damn I feel even older than I am now! (Or.. shit - I guess I am that old!)