Fennel is extremely good for digestion. It acts as a general toner for the digestive system and is particularly good for enhancing agni, the digestive fire, without aggravating Pitta. In India, eating a few toasted fennel seeds after a meal is a common practice, both to aid digestion and to freshen the breath.
In Ayurveda, cinnamon is used to balance the digestion. Cardamom is tridoshic (good for balancing all three doshas), but people trying to keep Pitta in balance should eat it in smaller amounts. Cardamom is considered an excellent digestive, especially beneficial for occasional bloating and intestinal gas.
Spices are ingredients in many synergistic Ayurvedic herbal formulations, and an Ayurvedic expert, when giving you advice, is as likely to recommend specific spices to include in your diet as to suggest herbal supplements for you to take.