The $15 OmniGraphSketcher is good for traditional diagramming, such as for creating precision graphs in architecture, finance, engineering, and space planning.
The iPad doesn't have a camera, so you can't show yourself in a videoconference, but you can join one conducted on the Internet by using an app from any of the major Web conferencing services. There are free apps for attending meetings via Cisco's WebEx, Citrix's GoToMeeting, and CallWave's Fuze Meeting. Of course, you need accounts on those services to host the meetings from a computer -- you can't host them from an iPad.
If you're using iPads as kiosks or public stations, such as at museums and schools, the $10 AVD Browse disables the iPad's Home button and restricts the available websites to prevent users from navigating away from the information you're presenting.
File management and printing
There are lots of Wi-Fi file-sharing apps for the iPad, and many productivity apps include such "air sharing" capabilities. Avatron Software's $10 Air Sharing HD is a good option if the built-in file sharing in your other apps isn't enough. The same goes for the $2 ReaddleDocs, which lets you collect Office, iWork, and PDF files from the Web, email attachments, and other sources for viewing, with extra capabilities such as extracting text from PDF files.
DigiDNA's $5 FileApp Pro is a file organizer for your iPad. It lets you copy files to and from your iPad, then organize, rename, move, and multiple-select them. FileApp Pro also allows you to open the files in compatible iPad applications.
Chances are you don't yet have an AirPrint-compatible printer, so the new iOS 4.2's print feature isn't usable. But you can print to many Wi-Fi-connected printers using an app such as EuroSmartz's $10 PrintCentral for iPad, which has you copy the desired text into the app, then prints that material. It also allows you to print to a network printer across your Wi-Fi network. (To print via your PC or Mac, such as when accessing non-Wi-Fi printers or printing via your computer over 3G, you need to install EuroSmartz's free WePrint printer server on your computer.) Other iPad apps that can print directly to Wi-Fi-connected printers include EuroSmartz's $9 Print n Share, Wellala's $5 Print Magic HD, and Readdle's $7 Printer Pro.
Cloud storage and FTP
Box.net and Dropbox offer free access to limited file storage in the cloud; for more storage, there is a charge. Using their iPad apps, several applications can retrieve and store files on their online servers for access by your other devices and computers.
Apple has its own MobileMe iDisk cloud storage service as part of its $99-per-user-per-year MobileMe service, which includes an email account and online calendar. The MobileMe iDisk app lets you exchange files directly with this service.