finding money
I was going to say - putting a coat on you haven't worn in a while and finding a fiver or a tenner in the pocket.
Also:
Walking into a busy, warm pub on a cold winter's evening.
The little rush that I get, no matter how many hundred odd times I've done it, when I walk up the steps into the stand at Anfield before the match.
Seeing a girl's boobs for the first time.
The first sip of a pint of Guinness.
The lights going down in a cinema.