Being a little of a freak about anything space, I enjoy working the ISS with voice or packet. Contacting the ISS is not as difficult as it may seem. With my humble setup I have worked stations via the packet digipeter as well as NA1SS via voice (from my mobile in the truck!).
Amateur Radio Frequencies (Note: Only one mode active at a time)
FM L/v VOICE Repeater (Worldwide)
AX.25 1200 Bd AFSK Packet Radio (Worldwide)
FM SSTV downlink (Worldwide)
UHF Simplex (rarely used)