R Micha Berger just posted an excellent essay on his blog, Aspaqlaria, on Gratitude.
Here is a quote to give you a taste of this must-print-and-read-on-Shabbos post:

What does “todah” mean? As it stands, it means “thanks”. The same root conjugated as “vidui” means to “confess”. Last, when the mishnah wants to stress that something is outside of a dispute, “hakol modim” — “all agree”. What do thanks, confession and agreement have in common?

To find out, click here.