Build a charcoal fire or preheat a gas grill. In a large, heavy saucepan, heat 2 tablespoons olive oil over direct high heat. Add the garlic, onion and cumin and cook until the onions begin to brown, about 10 minutes. Add the beans and beer; season with salt and pepper to taste and cook for 10 minutes, stirring occasionally. Mash the beans with the back of a fork and simmer, stirring frequently, until thickened, 5 to 10 minutes. Keep warm.
Brush the steak and corn with olive oil and season with salt. Grill over direct medium-high heat, flipping the steak halfway through and turning the corn occasionally, until the steak is medium-rare and the corn is blistered, 6 to 8 minutes. Transfer the meat to a platter to rest for 10 minutes before slicing thinly against the grain.
Using a kitchen towel, stand the cob on its end and run a small, sharp knife down the cob to remove the kernels. Break up the kernels and place in a glass or plastic bowl along with the tomatoes and their juices. Stir in half the lime juice and 2 tablespoons cilantro and season with salt. Set aside.
Season the reserved beans with the lime peel, remaining lime juice, remaining 2 tablespoons cilantro and salt and pepper to taste. Serve with the corn salsa and steak.