[b]Some people call emergency contraceptive pills "morning after pills," but you don't have to wait until the morning after. You can take the pills right away or use them up to five days after sex if you did not use birth control, you think your birth control failed, or you were forced to have sex.

You can use pills labeled for emergency contraception or certain brands of daily birth control pills to prevent pregnancy after sex.

Below are list of regular birth control pills (also called oral contraceptives) that contain the hormones researchers have found are safe and effective at preventing pregnancy in the few days after sex.

Oral Contraceptives used for EC / Progestin Only
Take 40 pills within 120 hours after unprotected sex:
Ovrette
Oral Contraceptives used for EC / Progestin-Estrogen Combined
Note: in 28-day packs, only the first 21 pills can be used
Take 2 pills within 120 hours after unprotected sex and take 2 more pills 12 hours later:
Neogynon
Nordiol
Take 4 pills within 120 hours after unprotected sex and take 4 more pills 12 hours later:
Lo-Femenal
Microgynon[/b]

Source: http://ec.princeton.edu/info/ecp.html