I'm planning on taking my partner and his family on a trip around the UK next year, and I have a ton of ideas in my head that I want to have written down in some form that makes it easy to edit and move things around. So I'm looking for suggestions for software that ideally makes it easy to enter information about transport and hotels, as well as thoughts on potential destinations, day trips, etc. I have used TripIt, but it requires me to be a bit too specific with dates and times, I want something that is more flexible and lets me brainstorm without pinning me down to certain things.
Check out http://Duffelup.com. It can help you to plan a trip including transportations, activities, logging, daily trips, or any idea/notes you may have. It allows you to write down ideas without specifying dates and times. But you can definitely plan those specific timings when you're ready. Hope this helps.
Edit: Mindmapping softwares like freemind might also work for you. But they are not specific for trip planning.
You may want to consider some kind of online note-taking software, like Evernote. It makes it easy to write notes, capture webpages as notes, etc.
If you own an iPad something like MindNode or iMindMap might be worth looking at.