I am using Todoist(.com). It's an app/website that should appeal to those that want a TODO list with some grouping features like 'projects' and 'kanban boards'
Each task/item can have optional flags and reminders that I use to remind myself that I am missing a hotel for a trip or a cancellation deadline for something is coming up.
There's not travel specific features or email import, but it's proven very useful and after testing the free version I upgraded to the paid one months ago.

I like the Flighty app on iPhone — just for flights but it has a really nice interface.

I use OneNote and have a section for each trip. I can “send to OneNote” from any email confirmations in Outlook and can scribble notes onto the pages with iPad and pencil. I sort the pages into the sequence of my trip. Sometime use CheckMyTrip in addition, which is reasonable for flight change notifications

I use TripCase. I find the UI a lot more intuitive than TripIt.

I use TripIt.

My employer uses SAP Concur for expenses, Concur owns TripIt so I was able to activate a free Pro subscription through Concur apps.

Also highly recommend TripIt. I love the timeline layout. The ability to add notes, activities, restaurants, etc. in addition to flights and hotels is indispensable.

+1.

Tried TripIT, but I like Excel better 'cause I can customize even with photo inserts & maps in JPG. Then print to PDF for my phone. Also a copy on OneDrive (with lock). Works for me since 2008.