Evernote is a free app (Mac/PC, iOS, Android) that is a great tool to save, and organize, files, information, images, etc. that you would like to access at another time. You can type text, add images (or take with your device), record audio, import PDF or other files, and more. It also has a great search capabilities, allowing you to find relevant notes by keyword tags, text within the note (or title), and even find text within an image.

Evernote for Educators - presentation highlighting some ways I use Evernote in my classroom, teaching, and personal life

Evernote also has some other free apps on Evernote's site -
Evernote Food - Organize your recipes you've saved/clipped with Evernote, or find ones already in the app. For iPad.
Web Clipper - Automatically save (clip) highlighted portions of a website directly to Evernote - free browser extension.
Clearly - View a web page without all the distractions
Evernote Peek - Create virtual flashcards for studying. Lift the Smart Cover for the clue, lift further for the answer, and pull down to repeat.
Skitch - Screen capture and annotation tool. Feeds directly into Evernote.