I don't read a lot of books about writing because I need time to actually write! And, frankly, many writing resources aren't all that helpful. But I found Hooked: Write Fiction That Grabs Readers at Page One and Never Lets Them Go by Les Edgerton to be worth the read. It delivers useful information not just about beginnings but also about story structure as a whole. Edgerton also offers plenty of good writing examples and practical tips. His down-to-earth style and sense of humor made this a fun read, too.