You can easily add any folder on your hard drive to the bookmarks menu of Safari, and it will open in the Finder when selected. Handy if you want to drag a picture from Safari to the Pictures folder or when you want to open your downloads folder without having to switch to Finder first. And very cool ... the bookmark menu will display the icon of the folder, even if it's a custom icon.
For example, for the top level of the hard drive, you would type 'file:///' and then drag the link to the bookmark bar. For your Documents folder, you would type 'file:///Users/yourname/Documents' and then drag it to the bookmark bar.
[Editor's note: The original hint specified using just ":///" as the URL, but I couldn't make it work unless the command started with 'file.' Also, do not hit return after typing the URL, as that will open the specified folder and then (at least on my two machines) blank the URL bar! Just type out the address, and drag the completed address to the bookmark bar.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030114063445783