I wouldn't recommend Sazón. It is used by many DR cooks but is very synthetic. The actual herbs and spices used in Dominican cuisine are preferable.
The more typical are probably:
Oregano - dried leaf AND ground - very unusual flavour, used to season beef, goat dishes.
Bija/achiote/annato - natural red colouring used in coconut-based dishes
Agrio de naranja - a bitter orange vinegar used as a condiment
Thyme, cilantro (fresh), aniseed, cinnamon and allspice are also popular for both sweet and savoury dishes.
Here's a nice, illustrated guide to Dominican spices in English:
The Dominican cook spice rack - Dominican Cooking
As well as mamajuana there are drinks like guavaberry and coconut and coffee liquers, and a whole range of natural fruit drinks like champola and morir soñando - check the desserts and beverages section in the Dominican Cooking site - although be aware that Dominicans tend to add far more sugar than our timid foreign palates are used to dealing with.
