For tomatoes, garlic, or a larger quantity of chiles you can use a stove-top grill such as the one shown below. This fits over a gas or electric burner. Sit the chiles on top and turn occasionally to allow even charring.
Use tongs to keep the vegetables turned for even charring. This does not work well for tomatoes because the juices drip through to your cook top.
Allow the chile peppers to sweat in the plastic bag* for about 10 to 15 minutes. When you remove them from the bag they will be easy to peel. Rinse the peppers under cool running water (wear gloves!). Peel the chile, remove and discard the skin, seeds, and the veins. (It may be desirable to have a small amount of the charred skin remain, depending on the dish. This can be a flavorful addition to fresh salsa).
*You may also use a paper bag but we find the peppers sweat more in plastic. You can even put your hand right in the bag and peel the chiles leaving the skins inside the bag.