Thai Herbs
Holy Basil (Bai Krapow) - The Thai equivalent of sweet basil, which can be used as a substitute for holy basil. Used fresh. 

Lemon Basil (Bai Mangrak) - The leaves have a smell redolent of citrus. Usually eaten raw as an accompaniment to curry. Its seeds are first soaked and eatened either as a dessert with sweetened coconut milk or as a appetite suppresant. 

Thai Basil (Bai Horapha) - Used in curries, its leaves have strong anise smell. Also known as cinnamon basil.

Cilantro (Pak Chee) - The root is used in curry pastes and marinade. The plant is used as garnish and flavoring, the seed for curry pastes.

Galangal (Kha) - A relative of the ginger, it looks somewhat like its cousin. The flavor is heavier than ginger, pungent. An ingredient of various curry pastes and a few other sauces. 

Ginger (Khing) - In Thai cooking ginger root is used in variou dishes. Young ginger is often pickled and eaten on the side.

Kaffir Lime (Magrut) - The leaves of this citrus plant (Bai Magrut) are used to flavor soups, curries, and other dishes. The fruit (Loog Magrut) is rarely available fresh outside of Thailand, its limited juice used as flavoring and a hair rinse. 

Lemongrass (Thakrai) - Only the lower part of this plant is used, which smells like lemon. If used whole, crush to release aroma. If to be eaten sliced very thinly, taking care to remove the tough outer layers.

Lesser Galangal (Krachai) - Long, thin brown roots with a pungent flavor. A main use for it is in Nam Ya, where it is a major flavoring agent after red curry. 

Mint (Bai Sala Nae) - Used fresh mainly in spicy Northern salads (laabs).

Spices
tumeric - related to ginger, it gives food a golden color and a slightly pungent flavor. In Thai cuisine, turmeric root is grated or pounded to release its color and aroma. Since raw turmeric is not widely available in the United States, we've used the ground variety.

Bird chiles - bird chiles although identified with Thai cooking, they're actually from South America

Garlic
Most recipes incorporate garlic, a seasoning familiar to Thai cooking since ancient times.

Thai Veggies

Straw Mushroom (Het Fang) - Available fresh in Thailand (beautifully large), but canned in the best. Used in soups and stir fries. 

Shiitake Mushroom (Het Horm) - Used in its dried form in Thailand. Has a strong aroma when dried, reconstitute before use. Suggested dish: Pla Neung 

Cloud's Ear Mushroom (Het Hoo Noo) - Adds crunch to stir fries and salads. Available dried, reconstitute before use. 

Thai Flavors for Cooking

Fish Sauce (Nam Pla) - Thai fish sauce is a clear salty brown liquid made from fermented anchovies, salt and water. Used in just about every entree in Thai cuisine, it amazingly does not add too fishy a taste. Common brands are Tiparos, Oyster and Squid.

Black Soy Sauce (Nam Siew Dum) - Made from a Chinese recipe, this thick soy sauce can either be sweet or not. The thick sweet variety is used as noodle coloring, in Chinese-style cooking and dips. Denoted by a blue cap.

White Soy Sauce (Nam Siew Kao) - Thin Chinese soy sauce, much thinner than Japanese soy sauce and lighter in taste. Denoted by a white cap.

Siracha Hot Sauce - Thick, sweet hot sauce. I like it on my Thai omelet.

Golden Mountain Sauce - Another soy sauce, but very aromatic, somewhat like Magi Sauce.

Oyster Sauce (Nam Mun Hoi) - Oyster flavored sauce thicken with corn starch and used in stir fries.

Shrimp Paste (Kapi) - Paste made from small shrimps and salt, pounded into a paste, fermented and dried. Toast slightly before use to give a warm aroma. Used in curry pastes, sauces, and a royal fried rice dish.

Vinegar (Nam Som) - White vinegar used in side salads and in Sweet & Sour.

Yellow Bean Sauce (Thow Jiaw) - A bottled sauce made from fermented soy beans. Used in Lad Na and stir fries. The Chinese variety is a good substitute, but the Thai variety is widely available.

Palm Sugar - a dark brown sugar made from coconut trees. Palm sugar is used in desserts and to add a hint of sweetness to savory dishes. It's sold in blocks and has a complex flavor, something like a mix of brown sugar, coconut and maple syrup.

Noodles

Rice Noodles (Guoi Thieu) - Usually sold dried in Oriental markets and must be reconstituted. Comes in different widths - wide, medium, thin, vermicelli. Recommended dish: Lad Na

Ramen (Ba Mee) - The Thais eat Chinese style ramen versus the Japanese variety. Ramen is sold fresh or dried in fist-size bundles that are given a quick dip in hot water before serving. Made from wheat flour and egg (thus the yellow color). Recommended dish: Ba Mee Moo Dang (Red Pork Ramen)

Somen (Kanom Jeen) - The rice flour dough of kanom jeen is first fermented a little before being processed into noodle form. This gives the noodle a distinctive flavor when served with curries. Sold fresh in Thailand in large plaited baskets separated with banana leaves. Recommended dish: Nam Ya

Cellophane Noodles (Wun Sen) - Made from mung beans, this clear noodle is sold in little bundles. Soak before use and add toward the end of the cooking process. Over-cooking will cause the noodle to get mushy. Used in soups, stir-fries and salads. Recommended dish: Yum Wun Sen

Dried Salted Radish (Hua Chai Po) - Dried salted daikon, quite unlike the Japanese daikon pickle takuan. Give it a quick rinse before using. Recommended dish: Pad Thai