Burbenog TD is a fantastic Tower Defense map for 2 or 4 players (best with 4). At the beginning, you vote for the level of difficulty (Easy, Medium, or Hard). You then choose from 12 different builders, who can each build towers with their own strengths and weaknesses.
From the loading page:
Choose one of 12 governors, each having a different set of available elements. Select from a total of over 80 towers, many with unique abilities, to prevent 40 levels of monsters from reaching the center. Purchase a Hero to catch leaks and use special abilities. Teamwork is necessary if you expect to win!
In this TD, you can send money to other players, who can build towers in your base and then concede (give) them to you. Easily one of the best tower defenses available.
Burbenog TD v2.02 466kb
To save, right-click on the above link, and choose "Save As". Browse to your maps directory and save there (usually C:\Program Files\Warcraft III\Maps\Download).