I was just reminded of another free Verilog simulator, so I though it might be useful to have a list:

Xilinx isim, part of zero-cost WebPack software (registration required, not open source, available for Linux and Windows)
Icarus Verilog (also at Sourceforge)
VeriWell Verilog Simulator
PVSim is a Portable Verilog Simulator for Mac OSX, Linux, and Windows with a GUI
Vcomp Compiler for x86
GPL Cver interpreted simulator
Verilator claims to be "the fastest free Verilog HDL simulator"

If I've missed any, I'll update the post. It would be good to hear about experiences with any of these.

See also jt_eaton's Socgen project
and Trevor Williams' Covered project for coverage measurement.

Cheers
Ed