For everyone's reference, I started a thread over on Vortex for people to post up pics and specs of their coilover setups. This way, users looking to buy suspension can see just how effective which models of coilovers are at lowering and also get feedback from people running the setups side by side in one thread.
Certainly lowering is not the only thing to consider when choosing coils, however it seems to be the biggest concern for most people. Other things to keep in mind are how well the coils ride, how well they make the car handle and how adjustable they are to allow you to dial in the exact suspension characteristics you want.
I'm just going to leave a link to let readers track the progress as more people contribute. Enjoy!