I have encountered this problem multiple times and it seems that a lot of people think that you have to recreate the publication / subscription in order to add articles. This is *NOT* the case.
It is actually a very simple task!
Right-click on your publication and click ‘Properties’
Go to the articles listing and uncheck the ‘Show only checked articles in the list’ box.
Now you can add a new table to your replication.
Next: The key step — go to the Agents tab inside of replication monitor for the publication in question. Right click on the Snapshot agent and select ‘Start Agent’. This will snapshot the table and send it across!
Questions? Comments? Leave a note!