Sailor Moon. All 200 eps, 3 movies, the Ami's First Love theatrical short, and the SuperS TV specials. I own all of the (poorly translated) Sailor Moon manga released in the U.S., but have yet to read them.
Oh, and someone mentioned the "lost" episode 67 (the one with Chibi-usa's dinosaur) and that they've only seen it in poor quality. I actually found a guy who did a fantastic fansub of it for me. All I had to do was mail him the DVD-R, and then he recorded his fansub for me and mailed it back. He did really well with it, too. He was also one of the most "legit" fansubbers I've ever seen; he required that I make a copy of the bottom of my season 2 box from ADV to see the proof of purchase so that I was a legitimate owner of season 2 who only needed episode 67 to make the season complete. He was really trying to stay as close to legal as he could get doing a fansub, which I thought was admirable. He said that he only wanted to help "true" Sailor Moon fans complete their TV episode collection, since that was the only episode unavailable to North American fans.
Sorry for the long explanation, but I thought I'd mention that. Carry on with the longest series discussion to stay on topic!
Oh, AND the whole manga, including Sailor V, but not including the 2 volumes of Chibiusa shorts (cause they seem pretty rare to find, including scanlations of them) :/ 
