I share many memories with those who have already posted. However my tuppence worth:
At Linton on a claggy winters day, being on the wing climbing up through the smeg with nothing to formate on but the references in the murk and then breaking out into glorious sunshine on top, breaking out into fighting wing and then tail chasing above! Brings a smile to my face as I type.
The general feeling of utter freedom that flying gives you. Joy at seeing things I would never get to see unless I was flying: various places in the Highlands that would take days to walk to, the number of stars out there when seen through NVGs, the beauty of the countryside (wherever you are in the world), parts of the Middle East that despite then tension and pain were a beauty and experience to see.
The feeling of success when you land from a mahoosive COMAO that your were instrumental in planning and leading (esp at night!).
The butterflies in your stomach as you run towards target (on the range or in anger), satisfaction of the release (ooer!), resounding thump as the carts fire the bomb off, and relief when it hits the target and goes bnag (for lives) and you know you've helped someone out on the ground.
All in all, I've been jolly lucky!