What do you do when "thank you" just isn't enough?

(And for the record, I'm asking this as a legitimate question.)

Let me clarify this as well: it's not the recipient of the "thank you" who thinks it's not enough. It's you, the "thanker", personally.

So what do you do? How can you adequately show what's in the depths of your heart, what's filling your soul from top to bottom? What do you do when you know--you KNOW--you'll never be able to repay the kindness? What do you do then?

How do you thank someone for the beauty brought to your world, for your renewed faith in blue skies and sunshine and endless oceans of promise and possibility? For filling your cup with so much joy that it's in a constant state of overflow, deep enough in which to swim? What do you do when words fail you time and time again, when it is absolutely impossible to express the immense gratitude you feel at every turn? When you're so consumed by said thankfulness and a refreshed sense of joy that you can barely think of anything else? When the very beats of your heart seem to resonate the words "thank you, thank you, thank you, thank you"? 

What do you do when "thank you" just isn't enough?

(And my heart says again, and my heart beats always, "thank you, thank you, thank you, thank you".)