By crossover, I don't mean Deadpool/Spiderman or Avengers/X-men. No I mean crossovers like JLA/Avengers or Judge Dredd/Batman. Some people like these kind of crossovers where universes cross over or merge. Overs DON'T.
Here are some of my favorites:
Judge Dredd/Batman.There has been a few of these printed. Thenones I have read are good stories, but like many crossover stories a couple of them start out like they have never met each other. The fights between Dredd and Batman are great. When Batman is arrested by the street judges and is interviewed by Dredd where Judge Death was. Batman breaks the bonds and punches Dredd square in the face. You also have the fight where Dredd is keeping Batman busy so he doesn't try to save some kids in a play, getting killed in the blast (Batman, Die, NEVER)
Batman/Captain AmericaSet in the past Captain America was sent to protect Bruce Wayne (I think?) but basically after a small fight between Bruce and Steve they work out who their are really fighting. This comic also has Bucky and Robin, who get switched. Joker joins forces with the Red Skull, well until he finds out Herr Skull is a Nazi. It ends with the death of the Red Skull and the Joker, unless they are immune to nuclear blasts.
Superman Vs TerminatorSarah and John Conner are on the run from the time travelling machines and are saved by the big S man. However this time the Terminators have help from the Cyborg (part Superman, part Robot. Don't know his name

). This is one of those crossovers where the universes are merged together as Superman is sent into the future where all the heroes died in the first week of Skynets attack.
Spiderman/BatmanThese two comics are great. The first issue is Carnage breaking Joker out of Arkham, but he is too late as the joker has been cured. That is until Carnage snaps him out of it, then it's Carnage who is the sane one in the team. Spiderman and Batman eventually join forces and defeat the pair. It has been a while since I read it so I will have to dig it out again. The second one has the Kingpin teaming up with Raul AL Gaul (May have spelt it wrong.) When I say team up, the Kingpin was blackmailed into joining R.A.G. Batman and Spiderman are trying to stop them and Bruce gets some info from Tallia. While Spiderman is secretly getting info from the Kingpin (the enemy of my enemy is my friend.) That plus Fisk knows you can't be a Kingpin if everyone dies.
Batman/PredatorA great comic where even though Batman is completely out classed he still goes in ready for a fight. He also uses the Bat-Armour. Darker than most of the crossovers I have read. Predators also pop up it a Superman crossover. But then you have a Batman/Superman Vs Aliens/Predators.
DC Vs MarvelI only have part of this Saga but the best part for me was where everyone was merged together. Batman/Wolverine (should have been Moon Knight) Captain America/Superman, Dark Seid/Thanos. The crossover I prefer is JLA/Avengers as I feel it had more of a story behind it. The final battle is also more dramatic with the Vision giving up all his stored solar energy to save Superman.
Well thats a few crossovers, just to get the topic up and running.
So what do you think about crossovers and which ones have you read?