SpectrumROM
Geoff Wearmouth's assembly file of the 48k Spectrum ROM.
I find this one much easier to follow than the Schoolkit variant, and it's been missing from the web for decades now. Will take it down if Hugo Warmtoffee objects.
Go here: https://zxdunny.github.io/SpectrumROM/SpectrumROM.html to view.