iOS: DocuSign Ink gets rid of the hassle involved with printing, scanning or faxing documents to sign by letting you open any document or take a picture of it with your device and securely send it. Best of all, unlimited signing is free.
DocuSign also notes a few important differences between its app and similar ones in the App Store: Your signature is secured and protected from being copied and reused, the app converts PDF fields so you can just fill them out and sign a PDF, and your documents can be stored on cloud services like Box.net or Dropbox.
The free app, designed for both iPhone and iPad, is available for download now at the App Store.
DocuSign Ink [iTunes App Store]