As you probably already know, the recommended size for working with textures in ZBrush (and most other 3D applications) is a power of two. For example: 512x512, 1024x1024 or 2048x2048. This will give the best results when calculating AUVTiles or GUVTiles UV mapping, as well as when texturing the model with Projection Master.
PowerOf2 is a very simple plugin that places six new buttons into the Texture palette. Clicking any of these buttons will immediately create a new texture of that size, ready to go.
To install this plugin, simply download the PowerOf2.zip file by clicking the link below, then extract it into your ZStartup\Zplugs folder. The new buttons will then automatically be available every time you launch ZBrush.
(If your ZStartup folder does not already have a Zplugs folder within it, create one. Do not place the plugin into your ZData folder.)