
Wireless flash triggers are a great innovation, proven by their popularity, but some people want that extra step in remote controllability. With new innovations in photographic lighting, there are now a range of options from which to choose allowing you to remotely control the flash power, modelling lights and more on your speedlights or studio flash units. Many of these solutions are system-specific, so unless you are a mad electronics DIY enthusiast or very rich, you must plan your purchases carefully.
Have we missed something? If any of the following information is inaccurate or incomplete, be sure to let us know in the comments.
Speedlights

Several systems for remotely controlling speedlights have emerged, including some which also work with TTL metering. Third-party triggers enabling remote controllability are often awkward as they have to be built around the limitations of camera manufacturers’ electronic and infrared flash signalling systems.
Preflash-based wireless system
Flash settings, including TTL, are sent from a proprietary flash or controller on the camera, via infrared signal, to a proprietary remote flash. The Radiopopper PX system can extend the range by relaying the infrared signals by radio, but this does not negate the need for proprietary controllers and flashes. Compatible third party flashguns are made by Nissin, Metz, Sigma and Quantum.
Pixel TR-331 and TR-332 Knight
Pixel Enterprise’s TR-33X series wireless triggers act a bit like a “wireless TTL cord”. The Nikon version (TR-331) supports TTL and allows you to use flash exposure compensation in camera. The Canon version (TR-332 Knight) has a few more features, allowing you to remotely set manual power levels on E-TTL EX II flashes.
PocketWizard ZoneController
Not yet released, the PocketWizard AC3 ZoneController will work with the ControlTL system (MiniTT1 and FlexTT5) and let you adjust manual power levels or TTL exposure compensation in up to 3 groups, using little knobs on the controller. You need a set of PocketWizard ControlTL triggers, plus the US$70 AC3 unit which sits in the hot shoe. For Canon and Nikon.
Quantum FreeXwire
The Quantum FreeXwire system transmits signals to Quantum Qflashes via radio waves. With different combinations of Qflashes, transmitters, receivers and adapters you can get full wireless TTL control, remote power adjustment, or both. Read more here.
RadioPopper JrX Studio
With a RadioPopper RPCube or 3-pin cable, you can remotely control the manual power levels of Nikon and Canon TTL speedlights from your camera. Adjustments are made via analogue knobs on the transmitter. Unfortunately RadioPoppers are not yet available outside North America.
DIY: RadioPopper JrX-style controller
With a bit of electronics know-how you can make your own radio trigger working on a similar principle to the Radiopopper JrX Studio (see above). More details here.
DIY: YN-460 control with a TV remote
This video and associated circuit diagrams show you how to modify a Yongnuo YN-460 so that you can remotely adjust power levels with a universal infrared television remote.
Studio Lights

Remote power adjustment is possible in some brands of studio lights with proprietary triggers and/or handheld controllers.
Bowens
Bowens has an infrared RC3 Remote Control Unit for Gemini R, Gemini Pro and QUADX lights, which features a built-in Pulsar transmitter. There is also a smaller Gemini Remote which works with Gemini R and Gemini Pro lights.
CononMark EID50 (EID500)
Here are some pictures of  an unreleased product from Chinese company CononMark. With IGBT circuit, AC/DC power, Bowens S mount and remote control, it promises to be a corker. UPDATE: The Comet mount version, NID50 (or NID500), has been announced. Read more about it in this article. EID50 will presumably be the Bowens S-mount version of the same light.
Elinchrom EL Skyport
Elinchrom Skyports can control the power and modelling lights of all Elinchrom flashes (except D-Lites) via 2.4GHz triggers. RX series lights can also be controlled from the computer with Skyport software.
Paul C. Buff lights
Alien Bees and White Lightnings can be controlled by cable with the LG4X. The same connection on the lights allows clever 2.4GHz remote control with the much hyped Cyber Commander. The Einstein has its own transceiver instead of the RJ11 jack.
Profoto Air
Like Elinchrom Skyports, Profoto Air allows you to control the power and modelling lights of compatible flashes, and has optional computer software.
RadioPopper JrX Studio
By plugging a RadioPopper JrX Studio into the RJ11 jack on a Paul C. Buff light (except Einstein), you can remotely control manual power levels from your camera. Adjustments are made via analogue knobs on the transmitter. Unfortunately RadioPoppers are not yet available outside North America.
Rime Lite XB Prime
The XB Prime system allows you to remotely control every function of your lights over ZigBee 2.4GHz signal, from the handheld controller or from your computer. What’s more, it can measure exposure, and recalculate settings as you make adjustments. Think of it like Paul C. Buff Cyber Commander meets Elinchrom Skyport, but with Bowens S-mount lights.
Visico LR Plus (aka Walimex VC Plus)
Visico Digital LR Plus (aka Walimex VC Plus) monolights can have every function controlled from up to 300m away with an optional 2.4GHz handheld remote. Available in the UK from Elemental.