My method is to do a full analysis of their company, and then make a very nicely formatted doc listing everything that I thought was bad, and a full explanation of how I would improve it if I were hired there.

Essentially, by using this technique, you've created a job for yourself, and given yourself value before you've even started there.

Then, when it comes to salary negotiation, you choose the highest available figure of their range and say with enormous balls that you're worth it because of all the things you can do for them - re your doc.

Works a charm for me every time.