The third one will be directed by someone else entirely. IGN mentioned the name of the guy, and I honestly can't remember who it was. This new Superman movie is going to keep Singer tied up until 2006, and Marvel isn't going to wait for him.
There's a Wolverine spin-off in the works also, but it's being brought into question whether or not Hugh Jackman will play the lead role in it. Honestly, I can't see anyone else playing Logan. I'm not a huge X-Men fan, but if they brought someone else in, even I would be livid.