One I made myself.
I've always played FPSes with the arrow keys for movement, starting from Doom/Quake and moving forward. Keyboards from that time were "101" key layouts, with no extra keys between ctrl/alt or anywhere on the bottom row. I've used that same style keyboard layout for forever, and I'm too stubborn to change now - no WASD for me. I've always used my pinky to reach keys for weapon switching, like the rightmost alt/ctrl/shift/enter/forwardslash/backslash keys, for example. Since I still play some FPSes, the layout was non-negotiable. I don't want to have to deal with pressing the Windows or print key.
When I was looking to upgrade to a modern mechanical keyboard a few years back (and PS/2 -> USB), I found that there were no "simple" keyboards that fit my needs - 101 key layout (ESPECIALLY no keys between ctrl/alt), no lights/displays, the proper physical key spacings, and so forth.
I researched everything for a few weeks, then I ordered all the parts and then built it over a few nights. I only wish I had found a MUCH heavier key - even the Cherry MX blacks (advertised as one of their heaviest keys) are too light compared to the old keyboard. It wasn't a model M, but was in the same class. If I find a heavier switch, I'll just have to de-solder the setup and install the new ones.
I still use the old early-90s-era PS/2 101 keyboard occasionally, but aging plastic and other components means that anything over real light use could damage some internal key supports again, and I've opened up that keyboard for repair jobs enough times to just not want to deal with that anymore.