Price comparison sites. Obviously they are good at aggregating opinions, reviews and prices.
Online Communities. Forums, blogs, etc where you ask the community for product recommendations.
Wikipedia. Most users do research before purchasing products and Wikipedia is fairly objective.
Amazon. It has become a knowledge library for lots of people who want to read product reviews, see ratings, find similar items, etc.
Consumer advocacy / testing labs. You know, unbiased sites that do more or less rigorous product testing.
"how do I fix my refrigerator?" "what's the cheapest insurance?"