Right now, some of your options in the App Store are:
Right now on the App Store, the maker of Memory Stick is offering its app for free for a limited time.
It is very similar to Datacase and Air Sharing. Although the description is a bit misleading, you NEED a Wi-Fi connection to upload files. If you don't have either Datacase, Air Sharing or another paid file sharing app I would suggest picking up Memory Stick for free.
Here are my thoughts on the apps I mentioned above:
Datacase: Bookmarking feature is highly useful. With a PDF that has 100 pages or more, bookmarking is almost necessary because scrolling through PDFs on any app seems to be more sluggish than any other file type. Page Up/Down and First/Last Page buttons are also useful.
Air Sharing: Has a slider to move faster through a document as well as Page Up/Down buttons. Makes use of the double-tap zoom in. Slightly better scrolling performance than Datacase.
Box.net: Best solution for someone who does not have Wi-Fi capability. No landscape mode. Storage capacity is 1 GB if you don't want to pay for more. There is also an upload restriction.
Memory Stick: Utilizes double tap for zooming in. Is currently a basic file sharing app.