Better Visitor Info

I need to be able to identify what companies are visiting our site so we can identify potential leads, the only way (other than forms & opt-ins) I can think of is to be able to see what company (not network) domain the user is on. For example, if a visitor working at Joe Doe Corporation browses my site, I would see that traffic came from joedoecorp.com.

I looked at a few plugins, and all it gives is the IP and what ISP network it is from; is there a way to leverage Google Analytics or a plugin to gather more accurate/detailed info?