NO$ZX81: A freeware ZX80/81 emulator for DOS and Windows.
T/S 1000 Emulation in a Browser Window: Java emulator of Timex-Sinclair 1000.
VB81: Sinclair ZX81 emulator written in VisualBasic. Runs under Windows on a 133MHz Pentium or better. Includes source.
XTender: ZX80 and ZX81 Emulator Site
Z80Stealth: A freeware ZX80 emulator for DOS which draws the screen lines by lint, thus fixing some flicker problems seen in other emulators.
z81: A freeware ZX80/81 emulator for Linux/i386.
ZX81 Emulator for the PalmPilot: ZX81 Emulator for the PalmPilot. Requires PalmOS V3.0 or greater.