Cooper Sportswear's A2 leather flight jacket in goatskin
One of the most historical jackets you can still buy nearly 100 years after they were first invented. Here are the details on the A2, and how you can buy one for yourself.

The A2 is probably the coolest historical jacket in existence today.
Primarily made from either horsehide or goatskin for their durable and resistant qualities, this military-style jacket has been in constant production (in various contracted forms) since 1931.

A successor to the A1 jacket with its button-up style and knit collar, the A2 is, in my opinion, a direct upgrade to the A1.
Watch my in-depth overview on A2 leather flight jackets
A design simple enough to dress up or down, it's hard not being able to style an A2 with whatever you happen to currently own.
Like most of the nice things I buy, I got this Cooper Sportswear A2 from eBay — the guy actually measured it to be 19 inches pit-to-pit and sold it for cheaper than they would typically go for (about $150 in this case after shipping and tax, and the P2P measurement was actually 22" — which is what a 42R should measure at).
For a new old-stock jacket made by Cooper, I would probably pay upward of about 260 USD for a goatskin but no more than that; once you start getting to the $300 range, you might be able to find pre-owned jackets from brands like Avirex in horsehide.
Just be sure to look at the paneling of the leather, as Avirex is much like Schott NYC: many of their jackets are flight- and bomber-jacket inspired, but aren't actually military spec or created for the U.S. military. Which isn't an issue, they'll be quality jackets, but if you're going to get an A2, I think the ones closest to the WWII contracts have the cleanest look.