Truecrypt Portable gives you secure enough encryption (in other words, if the NSA is after you, encryption is futile without much more thorough preparations; for most uses, this is quite enough).
Notepad.exe gives you text editing. (Or anything else that could edit text, really - notepad is Everywhere and is so stupid simple that it has no obvious flaws; its 54 kB character limit is essentialy a non-issue in hand-typed journals)
So, what I do with sensitive data: (create a Truecrypt encrypted container file the first time) - when unlocked, that container will appear as a new disk when unlocked - create a file in that disk - work on that file - lock the container again, done. This has the added bonus that the container is a file you can take with you (sync to Dropbox, put on a USB disk, whatever) and the content is secure.
Usual caveats apply: choose a LONG passphrase and don't forget it (there's no "password recovery"!!!), don't unlock the container on untrusted computers (malware snooping in is the biggest worry here), don't copy the sensitive file(s) outside the container.
(A single program that does both of these things is unlikely to do both of them well - and encryption is really easy to botch in many non-obvious ways. Therefore, I use one program for encryption, another for text editing. It's slightly less convenient, but much more flexible: e.g. if I decide that I want to use DarkRoom for text editing, I don't need to make changes to the encryption part. I could even store non-text data: images, GPS traces, sound clips, mindmaps; all that without worrying how it would fit with a text editor)