Was doing some wireframing for a job this week and found this very useful...
Paper browser by Rain Creative Lab — see original source
• Paper browser PDF template (Horizontal)
• Paper browser PDF template (Vertical)
For more resources that you can use in sketching phase of application development, geekchix.org has a bunch here:
A Collection of Printable Sketch Templates and Sketch Books for Wireframing
There's a lot of information out there on the inter-web about wireframing, Smashing Magazine has collated more than twenty wireframing articles, guides, and tutorials to help you improve your wireframing process:
35 Excellent Wireframing Resources