There’ve been many significant battles that would be interesting to watch - from a distance, I suppose. Some have been named and there are others - Agincourt, Waterloo and Normandy spring to mind. But we’ve got volunteers for the battle watch.
As we do for the lunar landing.
I think it would be nifty to visit the primordisl soup and watch the first living cell…, um, what? Coalesce?
I guess you could say evolve.
The Crusades. Most definately.
and Agincourt as well.
Krakatoa (at a safe distance with camcorders and lots of field vulcanologists)
Either Normandy or the Battle of the Bulge.
For me, I’d like to see them laying the last 5000 blocks of the Great Pyramid. Not only would it be cool to see them in their pristine state but I would also definitively know how they were built. Plus I could wave at the aliens as they flew away in their concrete lifting crystalline UFOs.
Forgive my ignorance, but wouldn’t that have taken decades?
For me, I’d want to witness something life affirming, something incredibly joyful. Something like the liberation of Paris during WWII. The victory parade passing through the Arc de Triumph, with everyone smiling and waving their flags – awesome! Can you even begin to imagine the party that followed?
The liberation of a prison camp would have been incredibly awesome as well but in a completely different way. Instead of having a loud, noisy victory, I imagine it to was an incredibly sober, quiet and reverent thing to watch those skeletal souls walk through those gates…free at last, free at last. Life affirming yet twinged with a bone crushing sadness.
Can I come too? 
Along similar-but-not-really lines, I’d also rather like to see the performance of Richard II commissioned by the supporters of the Earl of Essex, on the eve of Essex’s rebellion against Elizabeth… (obsessive? Moi? Never…)
I’d like to witness my conception.
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Er, uh… just kidding.
I wish I could have been in Potsdamer Platz when the Berlin Wall came down. I remember watching the CNN broadcast in my Junior High classroom, the genuine joy and exuberance on the faces of those people is something I will never forget.
Shortly thereafter, IIRC, Roger Waters came out of semi-retirement to perform “The Wall” live in front of a crowd of about 500,000. Must have been a great party.
The moment of the alleged resurrection. Personally, I think it’s bunk, so it would be nice to check that story out for myself.
The parting of the Red Sea. Such a powerful image.
Cannot imagine it could really happen, so it would be good to check out the reality - could be a bit underwhelming though!
I think it would be interesting (and very gruesome) to see one of those gigantor type battles back in the Ancient Rome days. I mean, imagine an army as far as the eye can see just whuppin’ ass … I can’t even picture the brutality. I don’t know why I would want to expose myself to unending bloodshed, but it’d be interesting.
I would like to accompany Darwin on the Beagle. Hold the seasickness and tropical diseases.
I’d like to be on the grassy knoll in Dallas on 11/22/63. If I could then have a “do-over”, I’d go over to the schoolbook depository and see what happened over there.
My second choice is Hitler’s bunker during the 1945 siege of Berlin.
When is St. Crispin’s Day?
I’m with Radiowave about the pyramids. I want to see how they were really built. The mathmatics involved are mind boggling could it really just be egyptians?
Atlantis would be a close second as far as confirming events goes.
I’d like to see the murders attributed to Jack the Ripper. I’d have to see all of them because some people think they were committed by different people.
I’d just like to know who.
I’d like to actually see the sinking of the Titanic, from the time it hit the 'berg until it sank.
I think it would have been cool to watch the Mediterranean Valley turn into the Mediterranean Sea a couple million years ago.
Similarly, it would have been fun to watch the “barriers” to the freshwater Black Sea erode seven-or-so millennia ago, and watch it become a much larger saltwater extension of the Mediterranean.