Protecting sensitive information like tax reports and business earnings is a synch with Espionage!
Now you can quit Espionage and use the folder straight from the Finder. Double-click on it and you'll be greeted with the password prompt. When the correct password is entered, the folder will be unlocked, and anything you put into it will be securely protected with the same AES-128 or AES-256 encryption that Apple's FileVault uses (actually, as of this writing FileVault only supports AES-128).
If you don't lock the folder, then it will be automatically locked for you when you logout or your computer is shutdown (whether it is forced or not).