This is a fun question to think about! Thinking about it reminds you about how you're contributing to the lives of others - and that's what you want. To focus on doing something that others value is a win-win for you AND the people who're thanking you, in such an empowering way (:
There are some things I'm thanked for in the course of my work and out of work, but after considering all of them, there's just one that I truly value the most:
When people thank me for being there for them.
I tend to feel helpless around people who're distressed, not feeling confident enough to say the 'right' things or feeling pressured but not knowing how to say things to make them feel better.
So when friends thank me for being there after talking to me about a worry they have, I feel incredibly humbled yet amazed that I made a tiny difference in their day - that something I said, or did, worked in transforming their mood or mindset. That someone experienced self-acceptance or empowerment after speaking to me, and the appreciation I receive is unexpected but it makes such a difference to MY day as well!
It's a two-way thing actually; thank YOU to all who trusted me enough to confide your worries in me. You gave me the chance to be there for you when you needed it, and I cannot say how much I appreciate your trust, that you invited me into your darkness so that I may fight it with you.
Colleagues, professors, and students at the educational institution (where I work as a researcher in motivational psychology) often thank me for:
Helping them to proof-read their thesis papers for the flow of ideas and grammar/spelling errors
Producing fluent pieces of academic writing
Handling operational/administrative tasks e.g. website management, budget management, project management
And in a small way, my baking has brought smiles to many people (: