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 $5 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.
The Google Docs online software toolkit lets you work on text and spreadsheet documents on the Internet from your browser. Unfortunately, it is very difficult to use on an iPad. Although several apps let you open documents stored in and send documents to Google Docs, the $4 GoDocs app from LightRoom takes it a step further, allowing you to edit those documents directly from your iPad. (You can also edit them in Google Docs-compatible apps such as Quickoffice and Documents to Go.)
If you work with your own or clients' websites and need to send files to and from, Headlight Software's $10 FTP On the Go Pro will do the trick. It also lets you edit Web pages and related files, so you can update your site when on the go from your iPad.
The free Citrix Receiver for iPad lets you run Office, SharePoint, and other data center apps on your iPad, through a virtual window to your Citrix-enabled servers. You of course need Citrix set up on the back end.
If you want to run applications on your Mac or Windows PC, or on remote servers, from your iPad, consider Wyse's $15 PocketCloud.
iCacti's $4 Server Monitor lets you monitor usage stats graphically for your Windows, Linux, and Mac servers, as well as network routers and printers. With Harlekins' $12 Server Admin Remote, IT staff can monitor Mac OS X Servers from their iPads.
The $30 LogMeIn Ignition lets you remote-control your Windows PC or Mac over the Internet. Another way to remote-control a PC or Mac and run its applications from an iPad is with the $6 Mocha VNC app. Hana Mobile's $5 Connect My PC is aimed at people who need to run just Windows desktops remotely from their iPad. Hana also offers the free Connect My Mac app. In both cases, multiple connections are allowed.
If you need to remote into SSH- and Telnet-based computers, Zinger-Soft's $10 iSSH can do the trick.