Sharepoint - How to Upload File to Sharepoint Via Commandline?

Believe it or not, you can use Windows net use to map a sharepoint library to a drive letter! Then you can use plain old copy or xcopy or whatever.

net use r: https://some.portal.org/documents [password] user:domainName\[username]
copy c:\somefile.txt r:\somefile.txt

Here is where I found that answer. I've done this, and it works like a charm. You can even specify whatever credentials you like, too.