CPU: Raxoft Z80 Test Suite - Exhaustive flag testing (TAP files)
CPU: ZEXALL - Z80 Instruction Exerciser (TAP/SNA)
System: ZX-Diagnostics - RAM, ROM, keyboard, interrupts (TAP/ROM)
ULA/Timing: Retroleum DiagROM - ULA, floating bus, contention
Contention: ZX Design Info - Memory contention documentation
Comprehensive: ZXSpectrum Tests Wiki - Complete test ROM/snapshot collection