Evernote
I would recommend this app because you can make notes with images and audio message in them. You can download it for Android & iOS.
Springpad
I would recommend this app because you can attach products and places to notes. You can download it for Android & iOS.
Bamboo Paper
I would recommend this app because you use your fingers to write notes. You can download it for iPad.
Dropbox
RECOMMEND-You can share files between your computer and phone. You can download it for Android & iOS.