My idea that I haven't gotten to implement yet: Make it possible for the user to get started without logging in, then force them to create an account after they've started playing around.
The particular application that I specifically want to try this on is going to be a document-oriented application. I'll let the user jump in and start creating something without creating an account, but then make the user create an account (or log into an existing account) to be able to save their work. If you've already spent even two minutes creating something, having to type in an email address and password seems trivial compared to having to start over again if they want to come back later. (That's the theory, at least.)
The key in my mind is to get the customer invested in the application (even slightly) before forcing them to make an account.