You'll need an appointment to have the copper IUD (ParaGard) inserted into the uterus within 5 days after unprotected sex, but it is the most effective form of emergency contraception. Contains no hormones, only a copper coil which creates a toxic environment for sperm. Learn more about the copper IUD. (link)
Next Choice One-Step
Next Choice the generic form of Plan B. Works the same way and also available over-the-counter without a prescription.
Plan B One-Step
Commonly known as the "morning-after pill", it is a single pill that contains a high dose of levenorgestrel, a synthetic progestin. Must be taken up to 3 days after unprotected sex to prevent pregnancy. Plan B is available online or over the counter at most pharmacies, and doesn't require a prescription.
Old school EC method that involves taking multiple combination birth control pills twice, 12 hours apart. Convenient for people who already have the right type of oral contraceptive on hand, but defintely the least effective form of emergency contraceptive.
Newest type of morning after pill that contains the drug ulipristal which blocks the actions of hormones necessary for conception. Must be taken up to 5 days after unprotected sex or failed birth control, and is just as effective on day 5 as it is on day 1. ellaOne is recommended for women who are closer to ovulation or are overweight. There is no age restriction but you'll need a prescription to get it OTC.