Formal:
* Enchanté(e) de vous connaître. (This is the most common and polite phrase.)
* Ravi(e) de faire votre connaissance. (This is also very formal and a good choice for meeting someone for the first time.)
Informal:
* Content(e) de vous connaître. (This is a more casual way to say it.)
* C'est un plaisir de te connaître. (This is very informal and should only be used with people you know well.)
You can also say:
* J'ai beaucoup de plaisir à vous connaître. (This is a good option if you want to emphasize how much you enjoy knowing the person.)
* Je suis heureux(se) de vous connaître. (This is a bit more direct and means "I am happy to know you.")
The best option will depend on the situation and your relationship with the person you are talking to.