Try this chile con queso recipe from celebrity chef Todd English. It's a great appetizer for Cinco de Mayo (or a nice cure-all the day after) and works well any time of year as a casual party dish for a tailgating event or potluck dinner.
Preheat the broiler with the oven rack 5 inches from the heat.
Place the poblano peppers, skin side up, on a foil-lined baking sheet. Broil until blistered, about 10 minutes. Place the peppers in a large Ziploc plastic freezer bag; seal and let stand 10 minutes to loosen the skins. Peel and chop the peppers.
Heat the oil in a medium-sized saucepan over medium heat. Add the onion and jalapeños and sauté for 3 minutes. Add the tomato and sauté for 1 minute. Reduce the heat to medium and stir in the flour. Cook for 1 minute, stirring constantly.
Gradually stir in the milk. Increase the heat to medium-high and cook for 2 minutes, stirring constantly. Remove from the heat and add the roasted peppers, cheeses, scallions, and salt, stirring until the cheese melts. Serve with tortilla chips.