Many recipes recommend using warming spices such as cumin or pepper with split pea soup. A hint of curry adds a pleasant "kick," according to one recipe from the cooking website Taste of Home.
The recipe on Taste of Home suggests using bay leaves, curry powder, cumin, freshly-ground black pepper and ground coriander for a warming soup.
A different recipe on the website Food seconds the use of cumin and freshly ground black pepper. It also suggests using cayenne and cracked red pepper if the soup is for people who enjoy spicy food. If serving to people with milder taste in food, just use celery salt and thyme.