The Webcomics Handbook.
Guigar has been doing webcomics since 2000 and is the founder of Webcomics.com, an online site dedicated to sharing knowledge with artists who are marketing and selling their work online. He is the co-author of How to Make Webcomics, a book I plugged earlier.
The value of Guigar's latest book is how incredibly specific it is. If you're looking to create a website with earning potential, Guigar will talk about various hosting sites and their relative advantages and disadvantages. He lists the various approaches to securing advertising for sites. He even has tips for speeding up page loading.
Guigar talks about the pitfalls of collaborating and how to avoid them. He has a chapter devoted to self-publishing, including information on print-on-demand vs offset. He has a chapter devoted to conventions and how to best present yourself at them as well as the economics of attending shows.
Other topics include copyright, contracts, insurance, search engine optimization, collectives, merchandise, and booth barnacles (fans who hang around your table at cons and monopolize your time without buying anything).
I have never seen a book about artists using the online world with as much practical advice. My only complaint is that the book lacks an index. However, that is a small complaint. If you have ever considered using the web as a revenue source, there is something in this book that will help you.