Design is hard enough without trying to reproduce a commonly used visual element. Here are some stencils that cover the basics.
Yahoo's GUI Stencils:
This is a fairly complete package of common web elements as well as basic viewports for handheld devices. It also has some nice "Windows" elements and the sizes of banner ads.
iPhone GUI Development:
Yahoo's stencil set has some elements for the iPhone, but this package gives you some additional iPhone options that aren't in the Yahoo package.
Web Browser Elements:
This package contains cursors and common web elements for a variety of browsers on different operating systems.
Loading Icon Generator (posted previously):