This is more for my own reference than anything else but today I was needing to enter a backslash key while using a US keyboard but with UK keyboard settings.
After trying pretty much every key on the keyboard in all combinations, I realised there was no key combination that would do this directly. Curiously it's a common problem and I found untold blog and forum entries that were not helpful. They basically said to change your input to US when using a US keyboard.
I figured there is always a way of entering a character by its code and of course this works. If you have a keypad, you can enter <Alt>92 and you'll get a backslash. That's all I needed in this case.