Kindle readers (who all paid a couple hundred dollars plus for their readers) are remarkably price sensitive, considering they've got to be mostly solid middle class and up, and they gobble up free books. Problem is they hoard much of it and a lot of it goes unread ultimately. I'm talking Kindle owners with hundreds of unread books purchased at cheap bargain prices plus the freebies. (I hang out on some Kindle forums so I know this is a very common occurrence.) But maybe you don't care whether the free stuff gets read?
I'd go with the free coupon idea rather than CD, but I don't think this plan will work until about 2012. Right now the ebook mkt is 2-3% of the total book market, but several sharp industry people have predicted it'll be a 20% share inside two years. There just aren't that many readers yet who ebook.
One thing I'm beginning to learn about the "book hoarders" is that continued promotion helps. You get them to buy or download it, then you remind them it's there. In the old days, standard marketing practice was to get your product in front of the audience multiple times before they buy. Well, now that the barriers are lower for each step, they may buy or acquire sooner, but we still have to do the same stuff to get them to _read_ and then it may take a little more visibility to get them to talk to others about it.
Don't put it all into one marketing method. Do it all. Be ubiquitous. That takes time and energy, but it's like critical mass - it adds up. Yeah, marketing could take up all of your time and energy but you can budget that time.
The other key is variation. You don't want everyone you meet to see the same blurb every time they hear of your book. Do interviews, do "about the author" notes, post short and interesting excerpts in blogfests or just on you own blog. Give them different kinds and levels of exposure.
I have operated a chain of "brick and mortar" book stores for over 25 years. In that time, I have used every marketing tool available and many more off beat from my imagination. The proof is in the product. A good product sells on its own merit. A bad product, even by a brand name, may sell out of the gates but falls off fast.
For a book, the cover and book title are tremendous tools to get the consumer to view the first page. If the product on the first page is good, the consumer may purchase. If it isn't good - it's back on the shelf.
BTW: My marketing budget is at an all time low and sales year-over-year are still increasing.