The iPad comes with a dozen or so built-in apps. But if you want it to serve as a passable substitute for a Windows or MacOS notebook, you'll need some additional ones.
Here are some suggestions, based on polling a number of business colleagues and other research. (Disclaimer: I haven't yet tried all of these yet.) There are about a dozen apps here, give or take; total cost, ignoring monthly service fees, between $60 and $100.
Consider DataViz's feature-rich Documents to Go Premium ($14.99), Apple's iOS versions of its MacOS iWork programs: Keynote (presentations), Pages (documents) and Numbers (spreadsheets), $9.99 each.
For even more PDF-wrangling, hedge your bets with Good.iWare's very popular GoodReader for iPad ($4.95), which displays, edits and even annotates PDFs and many other formats.
Picking a remote access app depends on what OSs and versions you will connect to (Windows 7/etc./MacOS/Linux); other features you might want; firewall considerations; and pricing.
And, says Clevenger, keep your eyes on Apple's iCloud, which will offer synching and other features, for example, as an alternative to needing a VPN for some tasks.
You'll add more apps over time, of course. But this should get you off to a good start.