Here are some other ways to express gratitude in French, depending on the situation:
Formal:
* Merci beaucoup (Thank you very much)
* Je vous remercie (I thank you)
* Merci infiniment (Thank you infinitely)
Informal:
* Merci bien (Thank you very much, more informal than "merci beaucoup")
* Merci de votre aide (Thank you for your help)
* Merci pour tout (Thank you for everything)
Specific situations:
* Merci d'avance (Thank you in advance)
* Merci pour votre gentillesse (Thank you for your kindness)
* Merci de me l'avoir dit (Thank you for telling me)
You can also add a phrase like "de rien" (you're welcome) after someone thanks you.