Kalypso has outlined a few bonus goodies for pre-ordering both the retail and digital versions of Tropico 5. The retail version is available as a "Limited Special Edition," and rewards anyone who puts down their cash early with an El Presidente avatar costume, and the Bayo del Olfato map for Sandbox mode. Plus, you'll get a Tropico passport and postcard in the box.
The digital version gets you a few bonuses as well. Pre-ordering on Steam nets you a 10% discount, a Businessman avatar costume, and the Isla de Vapor sandbox map. As more people pre-purchase, more rewards on Steam unlock. Those include a copy of Tropico 4, the first Tropico 5 DLC for free, and a copy of Omerta: City of Gangsters. If you'd rather forgo all that (and Steamworks features) for a bigger discount, you can get 15% off by ordering through Kalypso's own launcher.
Oh look, a new trailer. Isn't that nice.