If you are looking to discover open wireless networks I would look into netstumbler or airsnort. If you are interested in those you might want to check out knoppix-std, it comes with airsnort, and ethereal. It is quite a nifty tool I might add, it is a whole linux distro that runs off a bootable cd. I have no experience with any commercial sniffing software, but I believe that ethereal is a solid program as are many other free programs out there and you don't really need anything more than what you can get for free. I say this without checking out the commercial options out there, so maybe there is some awesome software that I have not heard about. You are just going to have to do some research on those, unless some more people reply with some good experiences with some commercial or non-commercial software. Whatever you choose, stay safe and good luck.