I consider that there are three great spectacular events to see in the sky. All are very rare, and I have not seen all three of them. Let us take a look at this :

1. Meteor Storm :

In 1998 I was looking to get to see a meteor storm from the Leonid meteor shower. It peaks every 33 years – with variations in the size of the peak.
Following the most common predictions of the peak I made ready to stay up for a night. But – as my luck (or lack of it) was – the show did not happen on that night . . . A slightly different, but even more spectacular show of a fireball meteor storm came one night BEFORE the prediction. Many people missed the opportunity, and so did I. A colleague of mine was up in the middle of the night and thought, “fireworks at this time of the night ?”. When he looked out there was one bright fireball after the other appearing in the sky.
The following night I stayed up, and essentially nothing happened. What a disappointment. Some people claim that it was the show of a century – and I missed it. On top of that – it was a clear sky that night, something of a rarity where I live.

2. Total eclipse of the Sun :

This is one event where 99.9% is *very* different from 100%. I went to see the show in Northern France in August 1999, and nearly missed the climax of the show. but minutes before totality a small blue patch appeared in the sky, and we got to see totality. Quite a spectacle.
I wrote a modest report on the event – with a few pictures, you can find it here.

3. Northern lights – Aurora Borealis.

In Denmark where I come from, I have seen the Northern Lights twice in my life.
Funny enough, moving further South to The Netherlands I would have expected to see less of it there. But in a shorter time span I have seen Northern Lights at least twice, and even photographed it. The photo is far from spectacular, but it will have to do for me.

Enter Norway – to be more precise, the town of Tromsø. There the auroras are a common occurrence. I came across a beautiful time lapse movie made by Ole Christian Salomonsen in Tromsø.
He publishes it (in HD Video) on his blog
I heartily recommend taking a look at the 4.5 minutes of movie, the aurora and his foreground images are – well – spectacular.