After generating my own private key, what's the proper way to add it to official wallet software? I've got some Go code that successfully generates private keys and vanity addresses as described by the wiki.

So I have all the parameters around the private key but I'm not sure what to do with that info to make it usable by the bitcoin core application.

Should I build a wallet.dat file to point the wallet software at? What's the format for that file? Is there an alternative format so I can import my new key alongside my old keys instead of replacing the existing file so that the software has more control of what the structure of the wallet.dat is?

I could layout the key in the same format that paper wallet QR codes use but I'm not sure what I'd do with that string for a desktop computer to accept it.

What format should I put the raw private key into and where should I put it for wallet software to use it?
In Core, go to "Help" and "Debug Window". Go to the console and type importprivkey [key]. This might also interest you: How do I import a private key into Bitcoin-Qt?