Princeton's Reproductive Health Technologies Project has a great chart of FDA approved emergency contraceptive pills (.pdf) currently available in the US.
Print it out, memorize it, and keep it handy! [May I suggest right next to your bed, you know, because there's nothing quite like whipping out a reference chart to enhance the mood.]
Two important things you should know:
1. Plan B, the two-pill packet, is being phased out (it's been discontinued). Don't be concerned if you cannot find it anymore. Use Next Choice, the two-pill generic instead or, even better, use Plan B One-Step or i-Pill / Nextime, the one-pill pack.
If you use Next Choice, disregard the package insert instructions to "take first tablet as soon as possible within 72 hours after unprotected intercourse and the second tablet 12 hours after the first dose". You should take both tablets as soon as possible after unprotected intercourse, up to 120 hours (5 days).
2. i-Pill / Nextime, the same as Plan B One-Step from Cipla / Paras, is available from (of all places!) Amazon for only $19.98.
Bottom line: If you are of reproductive age, sexually active and not planning a pregnancy, the emergency contraceptive pill should always be within your reach. Don't wait for an emergency to happen and then launch into a mad dash to find a place that stocks it. Be prepared and have the emergency contraceptive pill handy.