Scar is voiced by J. Michael Tatum, who also voiced Enel/Eneru in One Piece. Scar attacks state alchemists in the name of God... or, rather, he attacks in the name of himself.
In a bonus feature in volume five it shows that one of Ed's boxers' possible designs was Automail. In a volume 7 bonus feature, guess what the Truth takes from him.
Kind of a weird example of both Fullmetal Alchemist and Cowboy Bebop with the latter's episode Sympathy for the Devil. The Bebop episode features a character, Wen who essentially looks identical to FMA's Selim Bradley. This is funny because of the common twist that both characters are far older than they look and are only masquerading as children. While probably accidental, it means that if you watched Bebop after FMA, you'd probably guess the twist immediately, and vice versa.
Rewatch episode 19 knowing that Mustang and Lust are married.
Episode 15, Maes Hughes (voiced by Sonny Strait in the dub) says something along the lines of "What do you want me to do, fire my slingshot at him?!". Flash forward to 2007, and his voice actor became the new voice of the One Piece sniper Usopp...
Selim Bradley is introduced at the last second only to be killed off by the anime's version of Pride, King Bradley. Four years later, Selim Bradley turns out to be the manga's Pride. And King Bradley is his direct subordinate.
A similar case comes even later with Scar's death, where he continues to fight even after having his arms blows off. Come chapter 105 of that manga and not only does Bradley do the same thing, it was caused byScar.
There is a filler episode with Mustang's subordinates getting creeped out by unusual things happening in Warehouse 13, several years before SyFy had a show called Warehouse 13 about unusual things happening.