Terribear, are you interested in weight loss, overall health and longevity, or both?
The time-honored Mediterranean diet is well-documented to be one of the healthiest ones out there, with improved longevity and lower rates of heart disease, cancer (breast, uterus, prostate, and colon), dementia, and diabetes type 2.
The "GI diet" (there's more than one) may do the same; we just don't have long-term scientific data.
For weight loss, the Sonoma Diet by Connie Gutterson is Mediterranean-based and a good one. I've written a Mediterranean-style weight-loss book, but won't mention it here because that would probably violate the user agreement. But it's good, too. There's also a "Miami Mediterranean Diet" book that I've not read.