informal 

1. See you later.

2. See ya.

3. Bye bye

4. See you tomorrow.

5. Bye bye. Have a nice weekend.

6. Catch ya later.

7. Later.

8. Later dude. / Later dudes.

9. Take care. Bye bye.

10. Bye bye. See you next week.

formal

1. Goodbye. Have a nice evening.

2. Good night.

3. Goodbye. Have a good day.

4. Goodbye. Enjoy your day.

After meeting someone for the first time

1. Bye. It was nice to meet you.

2. It was a pleasure to meet you. Have a nice day.

3. It was nice meeting you. Bye bye.

4. Nice meeting you. Take care.

5. It was nice to meet you.

6. Nice to meet you.