First of all, congratulation to everyone who worked to have the private beta move public!
If you are active on other SE webiste, an effective way to advertise Economics.SE might be to add a little banner to the "About me" section of your SE profile.
Here are two templates, feel free to add more via answers :
Support the Economics.SE beta.
A good way to complement the banner might be to follow @EnergyNumbers and add a short list a of questions that you like.
Hopefully, that will contribute to help us move toward graduation.