Maybe I'm just still too inexperienced, but...

[Vanamonde]

I never get tired of putting something in a low orbit and watching the terrain roll by beneath me.

[KerbMav]

Doing anything right for the first time or even by accident, first smooth docking without half an hour of dancing around, soft landing close to a target location ... only two days ago I managed to fly a really nice gravity turn, creating a suborbital with an AP not to high and already spanning half the planet - after months of burning like hell, skipping through the atmosphere right after AP again, fighting to get an orbit that is not 75x548 km ... I felt like an artist!

[Javster]

What gets me right now is when you make a perfect slingshot off the mun and it turns out just with very little tweaking, your path heads straight to another planet.

Even when you screw up the slingshot.... this happens....

In my career save, I got a double encounter: Kerbin --> Minmus --> Mun --> Kerbin!