Car Amplifiers
Provides information about installation, reviews, links to forums and brands.
CarSound.net
Online car stereo magazine for audio enthusiasts and professionals featuring forums and a stereo knowledgebase.
Carstereo.com
Product reviews, forum, classified ads and online store directory.
eBuying Guides: Car Audio
Concentrates on where to shop for products, but also has staff-produced buying guides. Some of the guides are links to other buying guide sites.
Epinions: Car Audio
Consumer-generated reviews, buying tips and advice, ratings, price information, and searchable in a variety of ways from price to product type.
How to Buy Car Stereos
Gives general considerations on how to select a product and which features are useful.
Install Doctor
Car stereo installation resource. Step by step installation instructions complete with photos, tool list, and wiring detail, and a question and answer forum.