Connecting with the work
Since we've already seen how Textastic connects with various machines for file and code work, you might think there's no need for any other connectivity apps. But, brace yourself: not every file a developer works with is going to be text-based. You'll still need a way to access files like graphics and PDFs to read, edit, or otherwise use.
The best and simplest tool is the free-of-charge Dropbox app. Once you've signed up for the free Dropbox service, which gets you 2 GB of storage, you can access the contents of that folder from any machine that can see the cloud-base storage. On Windows, OS X, and some Linux distributions, that's through a dedicated folder in the filesystem that can be set to regularly auto-sync with the contents of the cloud folder. For the iPad, the Dropbox app will handle this functionality.
Dropbox is great for pulling files down to the iPad. It's not so easy, though, to get files into Dropbox if they're on your iPad, graphic files in the Photo Library excepted. Only an individual app with Dropbox support (such as the aforementioned Textastic) can push files out to your Dropbox, regardless of the installation of the Dropbox app. So, iWork apps like Pages and Numbers won't upload to Dropbox, but DocsToGo will.
For a little more two-way functionality, FTP on the Go Pro (available for $9.99) will connect to the Shared with iTunes folder, so you could move files into that folder and have them available in FTP to Go Pro. Still, like the Dropbox app, FTP to Go Pro is best for connecting with existing FTP sites and downloading and uploading files from there. Because it's based on direct connection to existing sites, FTP on the Go is suited for managing Web sites through straightforward FTP management.
All of these apps are essential starts to any developer's toolkit, enabling hackers to work with code wherever they might find themselves.