One of the biggest challenges with a new digital publication is how to get noticed. With traditional paper, businesses knew where to place it, mail it, wave the physical item under someone's nose. Getting seen becomes a whole new ball game with a virtual piece.
First, there is some overlap from the traditional print experience. If you are going digital with your annual report for instance, you already have your audience - now it's just a matter of converting them to the digital idea. I'm going to write out some meatier ideas on converting a print audience over to digital in another post, but to highlight a few options:
Let them know in advance with plenty of fanfare about going digital. "We're going green! Make sure we have your email by signing up today! Get our NEW environmentally friendly report in your INBOX rather than your mailbox. No more recycling!" Repeat the message in any items sent from your company and all your marketing.
Don't forget to mention the digital version within the printed paper version. Readers may check out the link and then enjoy what they see even more than paper if you have rich media and additional live links that allow them to explore ideas further.
To use more analogies from the print world in gaining new readers, you need to cultivate virtual "drop boxes" where readers can notice your digital editions easily. First step - create a splash on your website. You might consider an individual splash page for each publication if you 
have several niche publications or if you update a single virtual link over time. (Some digital editions keep the same link, but just update the content each time, rather than archiving a series of editions.) Another option, which I personally think works well, is to have a "library" splash page with the covers of several editions all available for clicking and viewing. Refer to this library page by adding a link within your publications, on other websites, within your signature, perhaps even in a print ad if you publish many digital issues. Another good option, if you have room, is to run the magazine covers as links down the sidebar of your usual home page. You can top off the column with an animated page flip icon for one of the publications. I encourage publishers to at least put one cover link and blurb about their publications on as many of their web pages as possible.
Other virtual drop boxes can include a Facebook page, other "library" sites (these are becoming more popular as digital editions are spreading), partnering websites, and web ads. Use the covers as a link when possible, or include the code for the animated cover. You can use the text for the url itself when you feel images may not be displayed properly.
There are also a few other ways to distribute your pieces that I consider outside the drop box idea - these are more social. The toolbars on digital editions almost always contain some social sharing and networking tools. Encourage business partners, friends, whomever is appropriate, to open your publication and share using those tools. These typically include an ability to email the whole publication or even a specific page, links for automatically posting to Facebook, Digg, and other social networks, and sometimes the ability to send small snippets from the pages to anyone who might find them interesting.
Don't forget to make proper use of your own email by sending campaigns about individual pieces or even a series of publications that might interest a certain audience. Ask readers who 
enjoy the publications to please forward along the emails. To increase your email list, include subscribe forms on both your website and within the pages of your publications. Don't be afraid to encourage subscriptions by pointing out how readers can easily stay informed with your digital versions rather than using paper, simply by signing up. Then, always be sure to give them great interactive publications with plenty of reasons to "go digital."
Finally, if you do have a series of interrelated publications, be sure to allow the search function to span throughout that archive. Put plenty of live links in one publication that lead to another, as well as to your websites or even directly to another publication's article. The more 
readers realize that they can truly have all your information at their fingertips from within the publication they are reading, the more excited they will be to use what you've published and pass it along. Plus you can save so much room by not having to type all that content again - just link to it! More clean, beautiful design allowing interactivity to do the work.
I'll add to these ideas as more come up and would love to hear from publishers and readers alike about ways they've discovered digital publications and had success in distributing them.