iAnnotate
Dropbox is another option. But if it is only one file, then email is probably the fastest and easiest.
If you are a heavy user of PDFs than iAnnotate is an ideal program for the iPad. iAnnotate transfers whole directories filled with PDFs at one wack. It has a strong file management system that you can take advantage of.
It also works with dropbox where if you pull the files down to the iPad you can also upload a copy that contains changes and markup notes back to DropBox so you can view the changed file on your desktop or laptop.
iAnnotae works over USB and wireless as well as email attachments.
The downside is that iAnnotate is $10 for the full package. It is worth every penny of it for what you get.
GoodReader is also useful and constantly gets beter. It is still $0.99 but I recently got an email from them and they are increasing their price to $3 or more.
I have most of the others and many not mentioned in this thread but these two are the best value, DropBox and GoodReader for working with PDFs. The file management system of iBooks and many other problems make it a distant thrid choice for PDFs IMHO. Everything else I have found is farther back and mostly not used anymore on my iPad.
Think of iAnnotate if you have heavy duty constant needs for PDFs and GoodReader for lighter infrequent use. A student who is heavy into PDFs will find iAnnotate a good value in spite of the cost.
Everyone should have DropBox. I have a half dozen DropBox accounts tied to various Gmail addresses. You can share directories between different DropBox accounts as well as across multiple different computers depending on your needs.
Click on the link in my signature to open a new 2GB Dropbox account and DropBox will bump that up to 2.25 GB for you instead of the default 2GB to start with. If you recommend DropBox to others and they gab a new account your DropBox will grow until it hits 10GB. Anything more than that you will have to pay for if you need more storage in the cloud.
Gmail accounts are neat because they give you 7GB of storage which works great for leaving your attachments online in an archive. You get another 1GB from that account by signing up for a Google Docs account too. I have over a dozen GMail accounts for various purposes. You do the math.
iAnnotate does a good job of managing multiple DropBox accounts for file storage and retrieval.
The one downside to iAnnote it will not upload a file to DropBox if it didn't download it from that location in the first place. GoodReader will send an alien file up so transfer the file from iAnnotate to Goodreader and upload it. Then if you need to massage it some more download it directly from DropBox to iAnnotate for future use.
iAnnotate can pull thousands of files at one whack from another computer using the AJI service. If you are doing this with big files it can take hours for the first transfer. The reason is that after pulling them down iAnnotate is indexing them so you can search inside the PDF for data from the file management menu. There will be an Apple spinning wheel on the top right of the program while all these new files are indexed. If you close iAnnotate it will pick up and continue the process later.
The files are indexed after the mass download takes place.
A copy of all files transferred are kept on the iPad and must be physically deleted or you can delete a whole folder of them at one whack.
iAnnotate can send the PDFs to just about any application that has registered as a PDF aware application. Many can send their PDFs to iAnnotate with iBooks being the notable exception. iBooks eats a file and keeps its copy. Bad Apple!
Don't forget to download Apple's iPad User Guide and Manual to iAnnotate so you can read it at all times, even without an Internet connection. iAnnotate downloads batchs of files at one time directly from DropBox. Aji downlaod from a desktop is usually across WiFi but if you are sharp iAnnotate includes instructions on setting up a transfer across the Internet from any computer in the world running AJI service. This could be one at a University and you could be on some beach with your iPad with no one the wiser.
