I second the hug thing, but other than that, happiness is...
...Hearing a funny joke
...Reading a good book
...Leveling up your RPG character
...Beating your friends in Street Fighter
...Watching a good movie, anime, etc.
...Pizza, fried chicken, hot and sour soup, hot dogs, hash browns, seafood, bacon...
...Getting a package in the mail
...Arguing (although I would prefer to use the term "discussing") a complex issue with an intellectual equal
...Sweet tea (homemade, of course)
...Finishing a tough workout
...Snow on the trees
...New clothes
...The moment when you find the answer to a difficult problem
...Well-deserved sleep
...Helping others
...Knowing at the end of the day that you are better person that you were yesterday
...Praying
...Catching someone's eye just to see if you can
...Plans that work
...Hearing from old friends
...Saying (or thinking of) something clever
...Sitting in front of a roaring fire
...Beach, forest, mountains, clean cities
As you can see, I'm easy to please