What are your favorite crossover ships?

This question comes from two recent things I watched.

I rewatched Power Rangers Time Force which reminded me about the cross over they had the next year with Wild Force, and how insanely good the chemistry between Eric and Taylor was, and how much it made sense for them to vibe.

To the point that with all the cool Power Rangers comics that have come out to explore the IP, including a Wes x Jen one, I still desperately want a Eric x Taylor graphic novel. I think that would be amazing.

The other is much more recent and MUUUCCCH more surprising, because whereas Eric and Taylor both come from the same franchise and one that was used to official crossovers between teams by that point, this one was out of nowhere from a movie that people in both fanbases where hesitant about.

I'm talking about the relationship between Jessica Cruz and Jaune Arc in the first Justice League x Rwby movie: https://www.youtube.com/watch?v=UrceiHCDRco&feature=youtu.be

Absolutely nobody, including me expected anything like this. But not only do they have really fantastic and sweet chemistry, but Jessica is also easily the character in the movie, and there relationship is the consensus highlight for very good reason.

It was a really fun surprise, and now I am invested and really hope they get to interact even more in Part 2.

So I was wondering, what other Crossover ships, particularly ones where the cross overs are official in some capacity are your favorites? The ones that actually got you invested in them?