This is a build I'm currently using in WvW. It's still undergoing tweaking.
Obviously WvW is more of an AoE type situation, which aside from shattering and few other skills, the Mesmer lacks. So ideally being a Mesmer in WvW our best roll is either all out single target DPS or utility. This build is more of a single target DPS build.
Second weapon is Staff with Sigil of Superior Earth. I feel that Null Field is interchangeable with Portal Entre depending on the situation. I also feel that Time Warp is interchangeable with Mass Invisibility depending on the situation.