Dropbox and Evernote are wonderful places to store your lesson plans. Drag your class folder into the Dropbox, for example, and then you will be able to open your lesson plan on your iPad or iPhone! Go completely paperless. Make edits to those lessons from anywhere, and they will always be up-to-date! Picture files with text become readable and searchable in any of the applications listed on this page... so after you take a picture of an old lesson plan, you can search the text!
You can also use Google Docs or OneDrive to store and share documents, including lesson plans! Both of these systems are wonderful for collaboration, as they have built-in document editors. This means you and a colleague or student can edit the same document at the same time, and you will be able to see edits as they happen! Deleted files are kept intact for 30 days before being permanently deleted (this is also true for Dropbox).