Chris Zurbrigg has released Blue Pencil: a new plugin that brings 2D drawing tools to the Maya 3D viewport.
Blue Pencil enables artists to use standard 2D drawing tools (pencil, brush, eraser, eyedropper) directly on top of the viewport. The resolution is independent of the 3D scene, and there is pressure support for Wacom users.
For animation, reference sketches and shot review
Potential uses of Blue Pencil include making model planning or layout sketches directly within Maya, and for animation work: the video above shows a sketched 2D walk cycle being used as a reference for a 3D animation.
The latter is supported by a set of dedicated animation features, including a configurable lightbox for onion skinning, and basic key editing and retiming options.
Annotations made with Blue Pencil are visible in Playblasts but not final renders, making it suitable for shot reviews, although the artist receiving your notes will also need to be running Blue Pencil in order to view them.
Blue Pencil is available now for Maya 2011 SP1 and above on Windows and Mac OS X, price $99. A Linux version is currently in private beta.