(in no particular order)
Old Car Brochure Project is a fantastic collection of brochures.
If they don’t have the brochure you are looking for, Hans Tore Tangerud’s lov2xlr8 website is often helpful.
Antique Automobile Club of America (AACA) judges any vehicle over 25 years old.
The Truth About Cars isn’t eighties-specific, but often covers eighties cars with an acerbic tone.
Autopolis is often an interesting read.
Curbside Classics does one thing and does it really well.
Ate Up With Motor features wonderful long-form posts with full model histories.
automobile catalog has terrific depth and detail.
Paintref.com helps me get my exterior colors correct.
Make or model specific sites that often have good content about eighties cars include:
AllPar covers all things Mopar with fervor.
Corvette-Guru is a great place to find Corvette information from people who actually drive them. I’m also grateful for their support of this site.
FerrariChat is full of folks who are very knowledgeable about all things Ferrari.
Excellence covers Porsche with careful detail.