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
Slinkys were invented by an airplane mechanic; he was playing with engine parts and realized the possible secondary use of one of the springs      .. More >>