Sinigang is traditionally tamarind based. Other versions of the dish derive their sourness from ingredients such as guava, calamansi, bilimbi, or unripe mango. Seasoning powder or bouillon cubes based on tamarind is also used in place of natural fruits.  Meat in sinigang (e.g., fish, pork, beef, shrimp, or chicken) is often stewed with tamarinds, tomatoes, garlic, and onions. Other vegetables commonly used in the making of sinigang include okra, taro corms (gabi), daikon (labanos), water spinach (kangkong), yardlong beans (sitaw) and eggplant (talong). Most Filipinos like to cook sinigang with green finger pepper in order to enhance the taste while adding a little spice to the dish. Note that sinigang is "Tagalog" in origin, thus the version one may see in the visayas and Mindanao regions may be totally different in taste (mainly because they opt to include ginger).
Sinampalukang manok or sinampalukan (from sampalok, Filipino word for tamarind) is not a variation of sinigang. What makes it different is the fact that the chicken has to be sauteed in ginger first as compared with the procedure in sinigang where you can put everything in the pot all at once and bring it to a boil. Sinampalukan is distinguished by its use of shredded tamarind leaves. It is made with ginger, onions, and does not have tomatoes or labanos.