One Piece, if I am correct. There is a bunch of other ones like Nana (47 episodes). Anyways, if its long then it needs to be a very interesting series. Nana fell into that category. Really great series, you should give it a shot. Clannad is another one with season 1, 2 and a movie! I would also recommend Hayate no Gotoku as it stands on 52+ episodes (season 1) and season 2 is currently airing as of now! Da Capo is really big as well, with seasons 1 and 2 around 50+ episodes, Da Capo II around 26 episodes (S1+2) and the new OVA that was just released. Da Capo is making big cash so the series will keep going, to what I hear.
I like short series to keep things flowing. But if the series is "really really good" and I felt it was too short, then I'd get somewhat depressed ... An example would be Toradora! For a 25 episode series, ... I dunno, I wanted more. I'd love to see some sort of spin-off or a continuation of the character's life (focusing on Ryuji and Taiga mostly) like Clannad to Clannad ~AfterStory~. I also felt Lucky Star was short as well, and Kannagi (2nd season will resume, tho we don't know when). There's too many to list.
For a 300+ episode ... I wouldn't know what to recommend. You pretty much named some good and bad ones. I don't watch kids stuff (Pokemon). Naruto and Bleach and One Piece are on my list. I'm waiting till they finish. I got a bunch of seasons from them.
I know D.Gray Man is over 100+ episodes and it finished! You can either purchase it (Funimation, blah) or you can grab a torrent from some websites. I got mine from a private tracker, hehe!
Enjoy.