Amazon.com and Kobo.
This is a book I picked up on impulse back in September and absolutely couldn't put down. I've been raving about it ever since too. After that, I was waiting eagerly for the next two books, Red Phoenix and Blue Dragon to come out, and buying them as soon as I saw them.
At $0.99, this is possibly your best chance to try a refreshingly different urban fantasy novel. I honestly feel that I can't say enough good things about White Tiger and it's sequels.
Lets put it this way. I have the paperback edition of White Tiger and I bought the e-book as well. To me, it's money well spent.