Another iPhone app: "Briefcase"
It does almost the exact same thing as the before mentioned “Folders” app (Allows you to browse and copy files from your computer without any desktop client). [Via TUAW]
UPDATE 10-01-08: Apparently this app uses Bonjour to connect to your Mac and has a native iPhone file browser rather than a clumsy web browser/web sharing to view and download files.
I’ve been using “iPhone Remote” aka Telekinesis to browse my Mac’s hard drive. It’s not nearly as elegant since it’s a Mac application (that must be running) that just creates a web server on your Mac allowing you to browse a “webpage” in Safari to access files.. It can be slow and annoying to view long lists of files.