In short: regardless of whether you're going (exclusively) digital, you want an agent.
Even if you fancy yourself a complete one-(wo)man show, an agent's multiple talents, myriad connections, and considerable experience will all be great assets to you in your quest for publication. This is true for more than a few reasons. In tried-and-true Bullet-o-Vision™ (I really should make a blog label for this):
· If you're dealing with an editor, an agent is worth his or her weight in gold in terms of contract negotiation (not to mention that going with an agent in the first place generally makes it much easier to get an editor's attention). This is doubly true as the details of e-rights are being hammered out.
· An agent will secure you a publishing house by way of said editor, meaning he or she is basically getting you editorial input, a marketing team, a publicist, a sales team, and an art department capable of making you a Truly Fancy Cover. Unless you're the aforementioned Jack/Jane of all trades, this is a huge bonus for you. (You also won't have to worry about getting your e-book fed out to Amazon, Apple, and the like.)
· You've got a buffer between you and your editor/publisher. This means that you can spend your valuable time writing while your agent spends his or her time talking to the editor/publisher (pitching your next project, hounding them for royalty statements, finding out why the awesome cover they helped you negotiate isn't showing up on Barnes & Noble's website, &c).
· You have a Fancy Website with lots of loyal visitors. Your agent has a Fancy Website with lots of loyal visitors. If you both add links to your book to your websites/blogs, you get that many more eyeballs reading about (and hopefully soon reading) your book. Agents go to bat for their clients in more ways than one.
· Finally, you get a measure of that e'er elusive brand recognition that separates your book from Joe "DIY" Lunchbucket. If you self-publish on-line, the only one vouching for your work is you. If you have an agent and an editor, you've got at least two organizations behind you vouching for your talent and credibility as a writer.