What is the best way to upload a file to a Document Library on a SharePoint server through the built-in web services that version WSS 3.0 exposes?
Following
Another option is to use plain ol' HTTP PUT:
WebClient webclient = new WebClient();
webclient.Credentials = new NetworkCredential(_userName, _password, _domain);
webclient.UploadFile(remoteFileURL, "PUT", FilePath);
webclient.Dispose();
Where remoteFileURL points to your SharePoint document library...