TB, Dutch Warmblood, or Trakhener are great breeds for eventing...TBs like everybody has said previously, and Dutch Warmbloods and Trakheners seem to just be well-suited to eventing in the warmblood world. They're both a little lighter than many other warmbloods, quick in action and brain, extremely athletic, and bold, plus with movement for dressage. We have one horse whose breed seems to be unique to him, although I don't know why because he is a fabulous eventer...he's an Anglo-Arabian/Oldenburg. He gets bone density and a sound mind from the Oldb side, plus quickness and stamina from the Anglo-Arab. He is a great mover and very bold, which I think comes from both. :)
He knows when you're happy; He knows when you're comfortable; He knows when you're confident; And he always knows when you have carrots.