Mac OS X: Show hidden files and folders in Finder

1. The easy way:

To show hidden files, just download and run this app.
To hide them again, download and run this app.
(Word of warning: Both these applications relaunch the Finder. So make sure you don't have any applications running, otherwise everything works just fine)

2. A little more geeky way:

To show hidden files and folders in Finder, open a terminal window and type this:

defaults write com.apple.finder AppleShowAllFiles TRUE

(the above sentence is all in one line), press return, and then type:

killall Finder
(and press return)

Finder will relaunch and you will be able to see hidden files and folders.

To revert (hide hidden items), type this in terminal:

defaults write com.apple.finder AppleShowAllFiles FALSE

(all in one line again), press return, and then this:

killall Finder
(and press return)
That's it!