Extra Scene In The Ending:

If you beat the final Night Elves mission on Hard mode, there will be an extra scene in the ending that shows what several Starcraft (and an Orc in a space suit) units would look like on Warcraft 3's engine. (Note: This is NOT a scene from Starcraft 2, it is just an example of what Starcraft units would look like on WC3's engine. Nothing more.)