Mobile Audio Related Sites
Elite Car Audio
One of the best ones out there, usually flame free
Has some of the most respected people posting here. Also has some idiots, but they are few.
Sponsored by Ampman Audio, the most popular place is the Adire Audio forum.
Smaller board, but alot of knowledgeable people. Home to the Elemental Designs forum.
Places to spend your money
More DIY stuff than you can shake a bent up coat hanger at
Authorized online dealer for everything they sell.
Unauthorized for everything they sell...but some of the best prices on the net
Dan Wiggins and David Hyre put together some of the best budget speakers around, including the Brahma
Ben is well on his way to being a car audio heavyweight
Awesome install stuff, but be prepared to drop the big bux