Bangkok's many temples are each unique and inspiring. If you can only see a few, pay attention to the star ratings and hit the highlights (Wat Phra Kaew is listed in the above section due to its location within the Grand Palace compound). But while the big temples of Bangkok are highly recommended, don't pass up smaller neighborhood temples where you have a good chance of learning about Buddhism in daily practice. Early morning is a good time to visit temples: the air is cool, monks busy themselves with morning activities, and the complexes are generally less crowded.
Thai people make regular offerings to temples and monasteries as an act of merit-making. Supporting the sangha, or monkhood, brings one closer to Buddhist ideals and increases the likelihood of a better life beyond this one. Many shops near temples sell saffron-colored pails filled with everyday supplies such as toothbrushes, soap, and other common necessities, and Thais bring these and other gifts as offerings to Buddhist mendicants as a way of gaining good graces. You may even see an early morning alms collection by (often barefoot) monks carrying their bowls around the neighborhood.
Small monetary contributions (the amount is up to you) are welcome at any temple. Devotions at a temple involve bowing three times, placing the forehead on the ground at the foot of the Buddha, as well as lighting candles and incense and chanting. Tourists are welcome to participate, but they are asked to pay particular attention to proper dress -- take off your shoes and avoid baring your shoulders, thighs, upper arms, or back.