Honestly, JL audio. For all the same reasons metioned above for the TC sounds website, which is also quite nice. The search feature in the JL gallery is quite nice. Links to all the discontinued products specs is cool, too. The fact that you really don't have to go digging for anything, it is all logically organized and linked, is really nice. No BS animations. No stupid muzak. The website is mature and classy. Let the product sell on its own merits rather than relying on F(f)lash to attract attention.
If I have to wait for animation to load, find a stop or mute button for annoying music or listen to some chick wearing so much eye makeup that she looks like either a raccoon or a hooker read from a script, I'm pretty well instantly annoyed.
Other annoyances I've found on car audio websites:
"This page currently under construction" for the last 2-3 years on the Orion website for pretty much anything other than the products page.
The RE and US Amps website auto resizing the browser when you use the dealer locator.
Pop-ups for everything on the Kicker website.
The messed up Javascript on the Exile Audio website (don't know if it's the script in general or an incompatibility with Firefox, but either way it doesn't work and if it's the latter then it's the only one I've come across).
Lame sound effects on the Image Dynamics website. A few broke links to the Team ID gallery as well.
Typos on numerous sites. If you're going to put up a web-page as your face to the world, proof-read the stupid thing.
Product pages that have the wrong text. They obviously made the first page as a template and then used that one to make the rest but they forgot to change the text so it describes something completely different than what the page should be about.
Broken links on a lot of sites, especially concerning links to the user's manuals. "Error 404: File not found" should not ever come up consistently on a commercial web page.