Home x5, Back x5 = Issue Tracker Popup.
Home x5, U, Rew x2, FF x2 = Clear the Cache - Most people think this is just a shortcut to reboot the Roku box, but it actually clears the cache then reboots. After you enter this code it will take between 10 - 20 seconds then the box will reboot.
Home x5, FF, P, Rew, P, FF = Platform Secret Screen.
Home x5, FF x3, Rew x2 = Secret Screen.
Home x5, U, R, D, L, U = Secret Screen 2.
Home x5, U, D, U, D, U = Direct to Wireless Secret Screen.
Home x5, R, L, R, L, R = Takes you directly to the Network page of Settings - Not a secret screen, but a handy shortcut!
Home x5, Rew x3, FF x2 = Bitrate Override Screen. - Works on my older Now TV box, but not on my newer Roku boxes. (probably not needed now most people have fast broadband.)
Home x3, U x2, R, L, R, L, R = Developer Settings - Has since been disabled in Now TV boxes, but still works on most Roku's. Allows you to 'sideload' apps onto the box, it was disabled in Now TV boxes since they thought it encouraged watching illegally downloaded movies and stuff... (many now tv boxes had micro sd card slots and/or usb ports & dev mode meant you could install a media player app.)
Home x3, U, L, R, L, R, L = Channel Info. Some boxes require Home x3,U x2,L, R, L, R, L
Home x5, D, L, U x3 = HDMI Secret Screen.
Home x5, FF, D, REW, D, FF = Antenna Secret Screen. In many boxes this simply displays the Platform Secret Screen again.
That's it folks, the full list!.