This is something obvious to anybody who really knows anything about plugin development (but it seems hard to quickly find a solution if you don’t know it already…). You created a wizard, made it known via the plugin.xml and it appears in New->Other->MyCategory. But you want it to appear directly under New (like so many other wizards…).

These shortcuts are bound to the perspective, so it is not a matter of finding the correct category id to have it appear there. You have to add a shortcut to your wizard in the wanted perspective. And this is one way:

<extension point="org.eclipse.ui.perspectiveExtensions">
    <newWizardShortcut id=""/>

targetID is the id of the perspective in which your wizard should be accessible via the shortcut. Using *, it is added to all perspectives (your wizard is really important after all ;-)). And newWizardShortcut points to your wizard via its ID.

Don’t forget to reset the perspective, after you have added this to the plugin.xml, otherwise the change may not have any effect. Now you can activate/deactivate the shortcut via customising the perspectives…