Some days ago, No Starch Press started selling an ebook version of TLPI. The ebook is also provided for free when you buy a paper copy of TLPI from No Starch (look here for coupon—valid until end of February—that provides a publisher discount for the book+ebook package).
Currently, the ebook is available only in PDF form and only from No Starch. However, a full range of other ebook formats is currently in production, and when those formats are available they will be sold through the usual retail channels (and made available to No Starch customers who already have the ebook). I expect those other formats to be available around mid-February.