PDF Browser Plugin: http://www.schubert-it.com/pluginpdf/
Allows you to view PDF files in browsers (and applications using the WebKit).
This feature will be/is built into Safari in Tiger, so this plugin will soon be unnecessary.
As for now, it's just OffTopic.
The latest version of Adobe Acrobat Reader (version 7, I think) includes a Safari PDF Browser Plugin (similar to it's Windows counterpart, but not as slow).