The following organizations provide valuable resources for drawing tools and templates that you can use:
4ourth Mobile
These are the templates we use every day for designing mobile device interfaces. Includes a numer of mobile components and additional information like typography, for general mobile design. Also includes gesture guidelines, vector handsets for all the major OSs, and a number of handset/OS specific widgets and icons. The illustrations and diagrams in this book were created starting with these components.
Adobe InDesign CS4 (.indd) format, compressed zip file, 15.7 mb
PDF for viewing, or opening in, Adobe Illustrator, et. al., 1.4 mb
If you are still working in Macromedia Freehand, the old (September 2009) version is still available. It has Little Springs branding, as that's who Steven worked for when he made it.
The actual document used to create the diagrams in this book has also been made available. Enjoy.
Adobe InDesign CS4 (.indd) format, compressed zip file, 55.8 mb
PDF for viewing, or opening in, Adobe Illustrator, et. al., 5.7 mb
Fluid UI
Fluid UI Also less of a design tool than a prototyper, where you do design in the tool. The design tools appear to be pretty flexible (you can do impossible things with the widgets) and has a reasonably large set of widgets to place on your designs.
Fireworks Wireframing Kit
Fireworks Wireframing Kit by Hannah Milan. Multiple templates, of different fidelity, as a series of downloads. Not all are mobile-specific (Fireworks, obviously)
Graffletopia
Mobile UI Stencils (Omnigraffle)
Justinmind
Justinmind Prototyper a UI design tool itself, but specifically designed to use pre-built widget libraries. Allows you to save your pieces, and share with a team.
Android 3.2 (Honeycomb) library items now available. As are many others, but I am not going to list them all, just the latest news.
Keynote
Keynote Kung-Fu Wireframe Toolkit For Keynote. Paid, but only $12. For multiple platforms, including desktop web.
Keynote mockups "sketch," wireframe and prototype took for Keynote (and I think Powerpoint and OpenOffice), free with a tweet. From Keynotopia.
Mobility
Mobility A free set of mobile UI design elements. (Photoshop)
Proto.io
Dedicated mobile prototyper of the type where they want you to do all the design in the tool as well. Can preview in more than the usual number of OSs.
Punchcut
Punchcut Toolset for Managing Screen Resolutions a collection of devices of various sizes, in PSD format, to assist with developing content or design at multiple resolutions.
Squetch
Wireframe Sketching Kit with tools for Browser, iPad upright, iPad landscape, Smartphone, GUI-Elements and Form-Elements. Not sure what some mean, but I guess "Smartphone" means they are trying to not just be iOS, so they get a category. (Illustrator)
Yahoo!
Yahoo! Stencil Kit many non-mobile parts, but also useful general and iPhone bits and pieces.