Just off the top of my head:
Poland has provided MiG-29s, and has recently agreed not "trade" more MiG-29s for Ukrainian drone technology and to be a partner in future development. The MiG-29 is a Soviet era plane, but Ukraine has used it well and it requires no retraining.
As for planes that have required retraining, the Netherlands supplied F-16As (probably much upgraded during Dutch service) and France has supplied Mirages (Mirage 2000s?).
Germany has provided Leopard 1 and Leopard 2 tanks, Marder IFVs, and Gepard armored radar-directed AA vehicles.
Germany and France have both provided self-propelled artillery.
The UK has provided Challenger 2 tanks and Storm Shadow cruise missiles.
Again, that's just off the top of my head. The US has been far from alone in assisting Ukraine.