Here are some solid, free journal/diary apps that I have come across so far.
The native "Notes" application that comes with the iPad is great for text, links, time stamping the note, and emailing the note(s) to yourself or others.
The interface and structure of this app takes a little getting used to, but once you play around with it you'll find that it has all the features of the built-in Notes application, plus the ability to add photos and geotagging (location). You can email notes with or without photos. There is a 140 character limit per note (ala Twitter). There is also a nice calendar view that lets you see your notes in both list and grid form. You can also add a separate number code lock protection just for this app.
My Secret Diary (free)
This app seems to have been designed for a younger audience (i.e. the pink binding and heart shaped lock you need to press to open it). That being known, the interface for the note pages is very easy to use. You can add photos and caption them, add sticky notes to the journal page, and even play your music library from the app while composing an entry. The only drawback is that you can't export or email the notes (yet?). Like the app mentioned above, you can add a second level of password protection to this diary.
Header photo by Robert S. Donovan