Naruto will end in early 2011, I think. I have trouble seeing it end within the next year because there are too many enemies left to defeat. Between the remaining Akatsuki members (including Sasuke), Danzou and Kabuto, there's still a fair amount left to deal with.
Bleach could go on forever. It has no plot and Kubo is basically just winging it and writing whatever comes to mind. It will keep going until he gets bored of trolling his fanbase.
One Piece has another 10 years left in it,easily. Oda is pacing it well, but it's such an epic series that it will keep going for a long time.
Reborn is one series that I really have no clue on. It could easily go another 5+ years depending on what sort of things Amano comes up with.
Prince of Tennis I think has another 20+ years in it, given the statement about the first series just being the prologue. This whole international competition will probably take 5+ years to finish, and then I can easily see the series going on to deal with Ryoma's next two years at Seigaku, and then when all of the characters have become pros.
Hunter x Hunter is impossible to tell because of Togashi's laziness. I think the series isn't even to the halfway point yet, so it has a hell of a long time to go.
Detective Conan is very difficult to tell. Aoyama has wrapped up certain things, but other things are still up in the air. Given that we still don't know Bourbon's identity and what happened to Akai, I think it's easily going to be five plus years until the series finishes.
Hajime no Ippo has another 10-15 years in it. Between Itagaki, Kimura and Aoki's continued growth, Takamura having another 4 weight classes to conquer, Mashiba's growth, Sendo getting to fight Martinez, Ippo becoming a world champion and actually confessing his feelings to Kumi, and the Ippo/Miyata rematch, Morikawa will be at it for a long, long time.
its toooo epic
