I like Travelpod. Like some others, you can use it offline - great for train journeys or nights in hotels with no wifi. I tend to use it to jot down notes about what we did each day (on my iPad mini) then after the trip, I just go on my desktop and do the whole journal thing after getting home at my own pace - with the option to share on Facebook and with contacts thru email.
Another interesting one is NoteLedge - it's more like a traditional journaling app (again, use it on my iPad). I used it to plan out our days before leaving on the trip rather then for daily journaling (I had TravelPod for that). You can draw in it, use your own handwriting as opposed to type (with a stylus of course, unless you are really good at making your handwriting look good on an iPad - I'm not). One thing that was helpful - we had to meet up for a walking tour, and I was able to use the navigator window on it to download a map of the meeting place, then paste it to the page...something that in the past I would have printed out and carried in a notebook with me. I'm sure it can do many other things, I haven't explored it too much. Mind you, I do still carry my 'made by me' daily book where I tuck away hotel reservations and tour printouts and whatnot, and gather up my entry tickets and receipts and things I want to save. But if I saw a neat restaurant (gelato places) or store (one in particular in Rome I wanted to visit) before leaving that I wanted to visit, I made a note of it and where it was located in NoteLedge.