To save you all the hours I just lost trying to get iVerilog and vvp working on OSX 10.7 here's how to do it.
Firstly don't build the stable version from source as vvp fails to build. Secondly Homebrew and Macports try to build the stable version and both crash with indecipherable error messages so they're out too. I haven't tried Fink but I'm going to assume that they're building the current stable version as well.
The solution to my woes? Installing the latest development version from the iverilog git repo. The following are a list of commands that will do that for you.
git clone git://icarus.com/~steve-icarus/verilog cd verilog git checkout --track -b v0_9-branch origin/v0_9-branch sh autoconf.sh ./configure make check sudo make install
which iverilog and
which vvp to check that they're installed. If nothing's gone wrong you should have a working installation.