Formal:
* Enchanté(e) de vous rencontrer. (This is the most common and polite way to say it.)
* Ravi(e) de faire votre connaissance. (This is slightly less formal than "Enchanté(e) de vous rencontrer.")
Informal:
* Ravi(e) de te rencontrer. (Use this with friends and family.)
* Content(e) de te connaître. (This is also informal and means "Happy to know you.")
You can also add a bit more detail by saying:
* C'est un plaisir de vous rencontrer. (It's a pleasure to meet you.)
* Je suis très heureux/heureuse de vous rencontrer. (I am very happy to meet you.)
Which one you choose will depend on the context of your interaction.