Moving files to the iPad with the Camera connection kit
If you use disk utility on a USB stick and format it to FAT32 then in Finder make the folder called DCIM. The images or movies have to be the file types that are supported by the iOS operating system. Do this and you can move files onto the iPad.
Some people say that the card readers can be connected up to the camera connection kit for the iPad, but when I tried it I got a message that said the card reader wanted too much power. So it may or may not work depending on the reader. It used to be possible to connect external USB microphones before iOS version 4.2 and the power management said no since the upgrade. That could be the same problem.
Generally writing files to external devices is not going to work but there are some work arounds. One is the $99.99 USB SD adapter, called AirStash that has support for WebDav. The iPad works well with that technology, you just put in the SD card and it creates a WebDAV share. With that you can get your files in an out of the iPad. The iWork apps by Apple, Pages, Numbers and Keynote will work with the WebDav as will GoodReader.
Good reader is a great way to move files on and off the iPad and it does such a lot, that it requires a full a discussion of its abilities. You use Goodreader as a way to get the files to other apps on the iPad using the Open With command. Goodreader will also link with MobileMe, GoogleDocs, Box.net, SugarSync, FTP servers and SFTP servers.
Another application I tried is called Padsync and not much success there. The list of applications you can send and receive files with is limited to the list of files that you can do the same with in iTunes. So I have to say after a quick trial with Padsync - What is the point?