Specifically, the letter U.
As it happens I do have a spare keyboard, however it has a European AZERTY layout and so is rather confusing to use when the computer is set to QWERTY (I can type on it as long as I don't look to see which key I'm pressing!). It's also got a horrid spongy feel to it, unlike the one I normally use which is a genuine mechanical switch-per-key model that dates back to the Windows 3.1 days.
Unfortunately there seems to be this massive gulf in the market between cheap nasty membrane/dome-switch keyboards at the low end and crazy expensive gaming keyboards with more bling than a chav's car. All I want is a decent switch-per-key model with a full-size layout, but I'm struggling to find one where I'm not having to pay an extra £50 for RGB backlighting or replaceable keycaps that I don't actually want. It's widescreen laptops all over again, where the marketroids have decided that what they think consumers want is more important than what consumers actually want and consequently ignored an entire market segment.