iPad: The iPad is a great tool for sketching out ideas on the go, and Forge is an app that makes that process a little easier by working less like a drawing app and more like a brainstorming tool.
Forge is made by Adonit (one of your picks for the best tablet styli) and unlike similar apps, it puts more of a concentration on brainstorming than drawing. You can save multiple drafts of drawings so you can iterate on ideas quickly and then see all those drawings on a big project board. That said, it still comes packed with a lot of adjustable brush sizes and colour palettes. The app's also free to check out, then $4.99 if you end up needing more projects.
Forge (Free/$4.99) [iTunes App Store]