We've got three entries today, because I screwed up when I made my initial list and left out Curse of Frankenstein! I know!
House of Frankenstein (1944), House of Dracula (1945); Abbott and Costello Meet Frankenstein (1948)
Oddly, my second-favorite Universal Frankenstein is the least-known one. Or maybe that's not so odd. Karloff defined the Monster's look, but when I look at Chaney and Lugosi in the make-up I can't really see anything but Chaney and Lugosi. I've only ever seen Glenn Strange out of make-up once (in The Mad Monster, which I highly recommend to anyone with a love of cheesy werewolves and mad scientists), so he disappears into the Monster role nicely.
His version isn't as thin as Karloff's, but he's got an awesome face for the part. He looks really cool and holds his own lumbering around next to Lon Chaney's Wolf Man and a couple of Draculas. In fact, thanks possibly to having access to Boris Karloff on the set of House of Frankenstein, he's much less out of place than John Carradine as Dracula in the two House movies. But I should probably save that commentary for next year (spoiler alert!). At least Bela Lugosi came back as the Count for Abbott and Costello.
The Curse of Frankenstein (1957)
Following the success of their first horror film, The Quartermass Xperiment (based on a BBC TV sci-fi serial), Hammer Film Productions began looking for other horror properties to adapt. Through a tentative partnership they were trying to form with a US studio, they got their hands on a script for a Frankenstein film. Unfortunately, it bore an unhealthy resemblance to Universal's Son of Frankenstein, but with some extensive rewrites and a different look for the Monster, Hammer was able to not only salvage the project, but create a genuine, ground-breaking classic.
The Curse of Frankenstein was the first color version of the story and also set new standards in the amount of gore that horror movies were allowed to show. Up until then, blood was rarely shown and when it was, it was obscured by the black-and-white film. With Curse, it was vivid red and the camera lingered on it. The film created countless imitators and launched a successful series for Hammer.
Tales of Frankenstein (1958)
The year after Curse of Frankenstein was released, Hammer struck a deal with Columbia Pictures to co-produce a Frankenstein TV show for US television. It was never picked up for a series, but it's interesting that its version of the Monster was visually a cross between Christopher Lee and Universal's.
Frankensteinia has a great history and synopsis of the pilot episode and notes that many of the unproduced script ideas became seeds for later Hammer films like Evil of Frankenstein and Frankenstein Created Woman. You can watch the entire pilot below