Wolverine 2
 

Although shouldn't it be called Wolverine 3?

Fox Reportedly Wants James Mangold, Hugh Jackman for 'Wolverine 2' - Comic Vine

Technically, but there have been several movie series that don't always follow their own naming conventions (the Mad Max trilogy, the Nightmare on Elm Street series, the Friday the 13th series, the Evil Dead series, etc).

Even the sequel to X-Men: First Class has a different name (and that sequel to the prequel is also supposed to be a sequel to X3 at the same time, further muddying the waters). It's like the Summers family tree, only with movies. ;)