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 favor for the other person in the future)

Fact
As late as 1820, the universe was thought to be 6,000 years old. It is now thought to be between 15 and 20 billion years old.      .. More >>