Upvote:1
Personally, I use two tools together when I want to plan trips with someone (or solo):
The first is TripIt, which you're already familiar with. I use it to track our itinerary and any confirmed reservations. Planes, trains, hotels, restaurant reservations, tours, sporting events, anything where I'm planning to do something at a certain date and time goes into the TripIt itinterary.
The other tool I use is Evernote. I'll create one or more notebooks for the trip and tag entries with the name of the relevant city or area. Evernote allows you to create checklists and lets you share your notebooks with your travel companions. You can clip web pages for places you may want to visit, even geotag them and place them on a map. You could set aside a notebook as a collaborative journal as well. The free plan would cover most usage as long as you don't save large files, but the $25/year plan is cheap and lets you download your notebooks for offline use.
This lets me keep TripIt focused on things I "have" to do, while having a notebook of places and articles of interest at hand in Evernote when I'm deciding what I "want" to do each day. While it's possible some tool would combine these two, separating your reserved itinerary from your notes is fairly useful.