Well i have had several...and its hard to pick just one out as i havent had kids or been married which usually seem to take the cake it seems.
So this isnt perhaps the best moment of my life as i really wouldnt be able to pinpoint that...
But when i was walking up the path to Borobudur i was struck by the absolute majesty of the place. It filled my heart and mind with utter admiration and awe at the ones who had made the place and at what it represented. As I reached the top where all those Buddhas are in those bell like formations...I was totally blown away. It still affects my life today because that was probably one of the most spiritual places i have ever been.
Now on a similar note i had the same sort of awed inspiration when i walked into the Sistine Chapel (regardless of the crowd) and St. Peters. The place was so majestic...so perfectly placed, so incredibly constructed that i felt that i was blessed just to have been there. They are both amazing structures.