Comparing Five iPhone File Transfer Apps - from TidBits
A good selection. I have DataCase and Annotator and have found that I use Annotator more often. It's incredibly easy - the iPhone doesn't have to be connected physically to my Mac [it will do the sharing and syncing via WiFi]. I save pdfs to a folder and then just sync its contents to my iPhone and then can read and notate the PDFs -- $4.99 at the iTunes App Store. The link to the developer's site with more information is here.