There has been some good discussion on GPL and dual licensing at matasanos blog, and ryan russell has also posted some good thoughts on this. This came right on time for me, as I've been debating lately what to do with a couple of projects I've been working on for awhile. I want to release the code, but it would also be great to sell and/or license it to companies wishing to use it commercially. These projects include a reverse engineering framework and some various network security tools. The RE framework is basically an engine written in C that securely and reliably parses, disassembles and stores massive amounts of data on any ELF object. It basically becomes usable by writing plugins for it. You can write output plugins (I will be including an HTML one with it) and plugins that hook the internal disassembler and ELF parsing routines. I have a couple of plugins ready and I want to release this code soon (1-2 months). So expect an open source version of that with a dual license for companies wishing to license it for commercial use.
** [ Start reading here if you came from bleedingthreats.net ] **
In other news, I posted a basic script today that parses the snort alert file for IP addresses and then queries spamhaus' zen real time blacklist. Feel free to modify and use it in your sensor network (its certainly not production quality as it is now). I am very interested in receiving modifications to the script and general feedback to the idea. I have already seen some interesting trends that I think will prove useful after a few days of correlating data. Enjoy!
Note: Spamhaus is unfortunately under DDOS as I write this though, so don't use it too heavily.
Update - I have posted a new version of the script - please contribute if you make changes