Many satellites carry X-band (7250 MHz to 7750 MHz) payloads - mostly for military communications. Some military payloads share a common spacecraft bus with TV type payloads, for example the Syracuse military payload aboard the French Telecom satellites. You are not likely to hear any clear audio or data traffic via these satellites, except for Sicral-1 which has two cross-strapped UHF to X-band / Ka-Band transponders. Skynet 5D has a nice UHF to X-Band transponder that relays lots of traffic. If you like exotic waveforms, then X-Band does offer the chance to see a lot of data modes in use. Typically the traffic is either frequency hopping, time / code division multiplex, PSK, spread spectrum or IP DVB-S/S2. You can however easily see these signals on a spectrum analyser or SDR. Details of X-Band receive hardware and ground segments have been split out into the X-Band Hardware page.
A sub-page on the British Skynet 5 satellites can be found here. Syracuse 3B information can be found here. A consolidated list of X-Band satellite beacon frequencies for satellites visible from Europe can be found here
The frequency lists above have been compiled from reception reports and off-air measurements. All frequencies in the list have been verified and were active (on the date given if that exists) under the satellite name / orbital slot position. If you are using these lists, please contribute with updates, which can be sent via email to info at uhf-satcom.com.
(above) Skynet 5D UHF to X-Band transponder