Detectives of Detective Comics: Slam and Speed

Perhaps first on everyone's list of the second tier characters from Detective Comics after the Batman Family (excluding long-underwear types like Crimson Avenger, Air Wave, etc) would be these two who appeared right from the start.

"Slam" Bradley and "Speed" Saunders... two early recipients of nicknames in comics for which they'd be forever attached. And they could not be more different in personality, while sharing many other common elements.

Slam was witty and gruff, Speed was serious and polished. While Bradley was a private detective attached to Cleveland's police department however loosely, Saunders was evidently a federal agent attached to the harbor patrol. Nevertheless, each adopted other identities and/or disguises to get up close and personal with the criminal element they wished to dethrone.

While Slam had a full-time loyal, albeit slightly incompetent, counterpart in Shorty Morgan, Speed typically worked along...his potential sea-side sidekick Red Pennington then occupied with the likes of Lt Commander Don Kerry of Anchors Away. 

Decades later, Bradley would work alongside fellow detectives of the same publication as Roy Raymond, Human Target and others cementing him on Earth-One. For Saunders, it was revealed later on that he was first cousin to Sheila Sanders (different spellings among their folks) aka the Hawkgirl of Earth-Two, with Speed remaining in retirement to let a new generation take up the call to action.

Along those whom Bradley encountered on his ocean vessel was the illusionist Richard “Mysto” Carter and his mammoth assistant Sihki. The pair’s counterparts Doc “Hocus” and Flannelhead “Pocus” were also illusionists, only instead of using slight of hand skills like Mysto, Hocus relied on the secret assistance of the Earth-Two Superman.

While Mysto and Sihki traveled around the world uncovering various mysterious criminal schemes using their power of illusion, Hocus and Pocus usually stumbled upon criminal activity which their friends Superman and Lois Lane assisted them in exposing.