Mabel, Maeve, Magali, Magdalena, Magnolia, Maia, Malia, Mara, Marcelina, Marceline, Marcy, Margaret, Margot, Marguerite, Maria, Marian, Mariana, Marianne, Maribel, Marie, Marietta, Marigold, Marina, Mariska, Marissa, Marlene, Marlie, Martha, Mary, Maura, Maya, Medora, Melania, Melanie, Melinda, Melisande, Melissa, Melody, Melora, Mercy, Meredith, Mila, Milena, Millicent, Mirabel, Mirabelle, Miranda, Miriam, Monica, Myra

Sorry, I'm sure some of these have been mentioned already.