The bulk of the final episode of 'Giant Robo: The Animation' (although if you want to get specific, starting from when Robo rises out of the wreckage again as Daisaku realizes he can't just stand by doing nothing anymore.)
What follows from that scene is, to this day, still probably one of those few occasions where I feel I can legitimately describe an anime as epic (...it's one of those hang-ups for me, I've seen the word used and misused so much I kind of had to up my standard for the word to allow it to keep any sort of meaning.)
Anyways, in non-spoiler terms, what follows is a final battle that, despite officially turning 10 years old this year, is still visually impressive to watch.
While a bit exagerrated, it's somehow strangely fitting that the soundtracks list the song that starts this chain of events as 'History's Greatest Decisive Battle'
...OK, ONE spoiler
OK...I'm done rambling