They do have a lot of choices! I think Parenting with Love and Logic explains everything in the most detail, but it will only appeal to someone who is willing to sit down and read a book. Painless Parenting for the Preschool Years is also very good. I was able to find tons of Love and Logic books, CDs and DVDs at our local library, which was great, because then I was able to try out several without shelling out for them. One other idea - I know you said you were interested in a book, but we ended up taking a Love and Logic parenting class through our local school. It was terrific, because it helped DH and I get on the same page with parenting techniques in a way that I don't think we would have if we had both been reading a book separately and picking out what we wanted to. I know quite a few of the school districts in our area offer these classes - maybe there would be something in your area, too.
ETA: I don't know what your religious affiliation is, but be forewarned that many of the materials have Biblical quotes peppered liberally throughout. Since the classes were through the local public school, the religious bits were stripped out, which for us was appreciated.