I'm not sure if this tip has been submitted a hundred times already, but just in case it hasn't, here it is. A really simple and fast way of viewing the contents of a folder sitting on your desktop or shown in the finder is to drag the folder onto an open browser window. As far as I know this works with all X browsers.
[Editor's note: I found this hint regarding navigating your hard drive with a browser, but nothing about dragging and dropping a folder...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020819021409597