PDF PROvider (US$6.99) for iOS is a rather complete solution that can turn just about anything into a PDF document for storing or sharing. PDFs can be annotated easily, and you get quick conversions of Office documents, Apple iWork documents, photos, contacts, maps and web pages in Adobe's Portable Document Format. A merge function lets you tie various documents together into a bundle, and the built-in web browser makes it simple to save a web page as a PDF.
The annotation tools included in PDF PROvider are first rate and easy to use, and you can add text, drawings, shapes, or other graphics into a PDF file. You can also sign a PDF -- important if you're filling out legal documents.
One thing missing from PDF PROvider is a scanner function, but you can add the capability as an in-app purchase for $0.99.
Using the app is very easy. As a test, I turned some photos and a map into PDFs. I added some text and a diagram and mailed it to myself directly from the app. The output was clean and readable from both a Mac and a PC, as well as my iPhone and iPad. PDFs can be shared via Dropbox and email, or they can be opened in other apps on your device that support PDFs.