Ultimately, you want to monetize this by building a list. That's the simple answer. If you're not doing that, you're shooting yourself in the foot.
But I would do two more things:
Number one is that I would do as much as I could to force the opt-in to your list before they get the ebook.
Number two is that I would assume that people are going to spread the ebook anyway. They're going to give it to their friends and family anyway, which means these new readers are not going to have to join your list to get your ebook.
So, you want a call to action within the ebook, too. That call to action can be, “Get your extra bonus here.” You can put that in the footer of every page of the ebook. Give them another opportunity to opt in and become part of your list.
Whether you're using a free ebook, to build buzz and spread the word around about a new product launch or you're just giving the book away to build your list, never neglect to monetize the back end.
What you do is one of two things: You set up an affiliate program and the affiliate program is ultimately giving away the free ebook and consequently, selling the back end to anyone who opts in to your list. I would make the back end a three-part teleseminar series, maybe.
Each part of the series could be one of three sub-niches. For instance, you may have an ebook about pets, if that's your niche. The first teleseminar could be all about dogs, the second all about cats, and the third all about fish, or whatever. If there's a ton of interest in one of those areas instead of all three, you can build a crazy home study course on one area. What I'm saying is what would happen if you did the "Your Niche Handbook"?
Do a teleseminar, get it recorded, and get it transcribed. Then, immediately do an "Ask" campaign to find out what people on your list want to know about your niche, and then get more people on your list by promoting the free teleseminar. At the end of the free teleseminar, you sell the as-yet-to-be-completed home study course—the three-part live teleseminar series.
You can also create an “affiliate product” for people with their own big lists. Allow them to brand the ebook and give it away to their list members. Allow them to use their affiliate links to the back-end product, which are embedded in the ebook footer. That way, your "affiliate's" list signs up to be on your list, the affiliate makes money on the back end and everybody is happy.
At the end of the day all it comes down to is...
Free ebook?
Get it out there, immediately upsell those who opt-in on the thank-you page—give them a one-time offer or something like that, the teleseminar series, or the course.
However you're doing it, it doesn't really matter. Whoever you're applying the information to it doesn't really matter—the model is the same. The reason I'm telling you to do it this way is because when you give people free information, upsell them to paid information. That's it—that's all it comes down to.