Yeah, as for free, Keychain Access is the one to beat.
I use MacJournal because I have it already. The thing you have to remember though is that 128bit encryption with a "regular" password is crackable within a very short time these days. 256bit with a "hard" password at least gives you the security that only the government will be able to read your data within a reasonable time frame. All depends on your needs.
Another option is to create a text file and store it within an encrypted image.