Favorite mail order, car parts catalogs (NOT SUMMIT'S, OR JEGS...
PAW was a mess when they quit... so was Speed-o-Motive... so many horror stories of unbuilt engines, parts not delivered, etc.
I've been buying from Northern Auto Parts for years... mostly engine parts. Redoing the wife's Jeep right now with parts from Northern.
I use Rock Auto's online catalog for reference material. They are 100 miles from me but the shipping costs's are stupid... often more than the cost of the parts! 99% of what I buy I get at my local parts store... great service, good prices and friendly people.