CEPro shows ten ways to turn iPhone into remote control. Another two-three are added in the comments. Personally I like two of them – solution with Global Cache iTach and XMBC Remote App.
Global Cache offers devices to control devices via IR, COM or relay by sending command via TPC/IP network. The GC100 is one of the popular Global Cache product. Now company offers a new line low-cost specialized devices iTach. For example, iTach on the picture can receive data via WiFi and transmit it via IR which allows to control IR equipment from iPhone.
XMBC Remote App will be useful for all XBMC users. It offers not only playback control of HTPC but additionally shows all information about movie, TV show or audio track. Also using that application it’s easy to navigate, play and pause music without turning on TV.