For most of the '90s, Booster Gold and the Blue Beetle were Those Two Guys of The DCU. They practically never got up to anything important of their own, but often showed up in team books or other heroes' series, where they invariably got into trouble thanks to some Zany Scheme or another. This came to an end in the '00s, when DC remembered they were both heroes in their own rights, Beetle died heroically, and Booster went on to star in his own series again.
This is because they're the characters most associated with the Keith Giffen era of the Justice League which occurred shortly after the characters were introduced to mainstream DC Continuity and which brought them to prominence. The light hearted nature of that series became associated with those two guys.
Similarly there's Beatriz DaCosta, aka Fire, and Tora Olafsdotter, aka Ice.
Sam and Twitch, NYPD homicide detectives, from the Spawn series. Sam Burke was a large and headstrong man, with a tendency for foul language. "Twitch" Williams, on the other hand, was thinner, bespectacled, and was usually the brains of the group.
Peanuts' Patty and Violet. They're the two generic girl characters from the early decades of the strip and enjoy tormenting Charlie Brown by, for example, telling him they're going to throw a party and not invite him. The two almost always appeared together, except sometimes when filling out crowd scenes or setting up punchlines for other characters. Their appearances decreased significantly in the 1970s, and by the 1980's, they had almost vanished. Not to be confused with Peppermint Patty and Marcie, who could almost qualify as Those Two Guys if they'd have less distinct personalities.
Frank has the Jerry Chickens, a group of chicken like creatures whose bodies are based on different geometric shapes.
Metropolis police officers Maggie Sawyer and Dan Turpin from Superman probably qualify.
Officers Thomson and Thompson from Tintin, of the "they look exactly the same" variety—except that one of them has a slightly curly mustache, while the other one's mustache is straight.
In the German comic Werner: The policemen Bruno (the fat one) and Helmut (the long, thin, stupid one)