As many environmentally-friendly shoppers soon discover, going green costs some serious green.

Eco-friendly products come at premium prices. A 2008 Honda Civic Hybrid, for example, will set you back close to $7,600 more than its conventional counterpart. Meanwhile, a gallon of Safeway-brand organic skim milk costs $2 more than the regular $3.99-a-gallon skim. In some instances, it's easy to argue that the extra expense is worth it: The hybrid Honda, for example, gets an extra 15 miles to the gallon and the organic milk doesn't contain potentially harmful pesticides, antibiotics and synthetic hormones. But that's not the case with all green products. While some are downright overpriced, others have yet to prove that they will beneficially impact the planet.