Seeing or petting a bird
Seeing a rainbow or anything where the colors are lined up in rainbow order.
Drinking cold water while in the shower (sounds crazy, feels amazing)
Going down a slide
Making children laugh
Hugging a sad child until they're not sad anymore
Playing the piano and singing my heart out
Singing opera until I'm physically exhausted
Shopping for arts and crafts right after pay day
The smell of chocolate chip cookies
Laying flat on my belly
Creating an especially impressive craft
Sketching
Seeing a Chinese character and knowing what it means
Seeing a happy baby
Research binging
People asking for my advice
Being asked to explain more about something I'm passionate about
Being recognized for my achievements
Listening to anything by Eric Whitacre
Weather that doesn't make me sweat
Looking at funny pictures
Reading 'Tumblr gets deep' posts
When something I write becomes popular or gets comments
Successful baking
Hearing a new song, falling in love, and then feeling excited that I get to obsess over it for days.
Eating, drinking, and writing in Starbucks and feeling inappropriately productive about the whole ordeal.
When people tell me their secrets
That moment when I've officially memorized a song
No migraine and no allergies at the same time
Feeling really connected with an animal
Being engrossed in a good book (starting and finished are different stories)
Being taken on a motorcycle ride by my best friend
Looking back and feeling like I've accomplished a lot
"Founder's Favorite" from Cold Stone with almonds instead of pecans. (I could eat this daily, haha)
Bedtime!
There are probably more but I tried to come up with everything I could think of. This was a great question to provoke some personal insight and thoughtfulness. Thanks for posting!