Amateur radio operators interested in contacting the International Space Station (ISS) can get a list of frequencies from the ISS Fan Club web site.They also have a section with audio recordings of previous contacts.
Another source for ISS frequencies is from the AMSAT ARISS page. It also contains the following instructions to increase the chance of a successful contact:
To work ISS from your home, you should have at least the following Amateur Radio equipment. A 2-meter radio with an output rating of 5 watts or more. While it’s possible to operate with an omni-directional antenna and even a whip, a small beam antenna similar to the Arrow antenna works much better and will increase your chances of success. If you plan to operate in packet mode a standard 1200 baud AX.25 TNC should be used and connected to a computer running APRS or other packet communications software.