1. Thanks

2. Thanks a lot

3. Thank you so much

4. Thanks a million!

5. Thanks for your help./ Thanks for helping me.

6. I really appreciate it.

7. I'm really grateful.

8. That's so kind of you.

9. I can't thank you enough (for extremely important things)

10. I owe you one.

(this means you want/need to do a favour for the other person in the future)