At the risk of sounding nauseating:

Topping out on a particularly tricky climb;
Learning a new tune and it actually sounds like a tune when you play it;
Dancing with a bloke who makes you think "wow, if he can dance like that, what else can he do so skillfully?";
Getting 2 aces in the hole and another on the flop alongside a nice pair of face cards - or another ace;
Going for a quick drink after work with your mates and getting home at 7am the next morning after staying up all night laughing and getting blootered;
Running and running and running;
Coffee;
Red wine;
Digging with a mattock on a crisp sunny morning with the smell of cold soil in the air;
Buying shoes;
Cleaning the cooker with baby oil.