At my private middle school, we use Ecce Romani. We have it as a required class, so I wouldn't know about learning it by oneself, but it's nice because it allows you to figure out some of the grammar by yourself before learning the chart. I think they might actually use it at the CTD course DeeDee mentioned, but I couldn't find an explicit statement about that anywhere.
Also, through the CAFE library system in Wisconsin (I'm assuming you're there because of your username) you can find some good resources. Most of them require a library card, though.
