Thanks to the events of the upcoming Civil War 2X-Men: Schism, Marvel is canceling Uncanny X-Men. Issue No. 544 is the end... at least until a bunch of new X-Men titles with new No. 1s come out.
As Comics Alliance notes, this, combined with DC's renumbering of its superhero titles, means the longest, continuously running comic published by either Marvel or DC is DC/Vertigo's Hellblazer, currently up to a heady issue No. 280.