I don't want to say Secret Six is the best book DC is publishing today, but it's hard to come up with any that are better. The book started as an Infinite Crisis spinoff, and has outlasted every other title that came out of that crossover. It's featured a rotating cast of characters, all of whom have been written well and are fiercely interesting - and while you can't build a complete team (or even collect the core membership), there are quite a few members who are available.
The original incarnation of the team, introduced in Villains United, comprised:
They were overseen by a mysterious character codenamed "Mockingbird." Fiddler was killed after their first mission, and was replaced by Catman. Cheshire betrayed the team to the Secret Society of Super Villains, and Parademon was killed when he detonated a series of Mother Boxes he had strapped to his own body as a living bomb.
The second version of the team appeared in the Secret Six miniseries.
Mad Hatter was kicked off the team (and a roof) by Ragdoll, and he was briefly replaced by Harley Quinn, until she reformed. Knockout was killed with the rest of the New Gods. The team broke up for a time, but eventually re-formed to break a former hero out of Alcatraz.
They were short a member until they picked up Jeannette, a new character who was eventually revealed to be a banshee. After several missions went bad, Bane took over the leadership, and his first action was to remove Scandal from the group.
When Catman left to search for the men who killed his son, Scandal, Ragdoll, Alice and Deadshot went with him, leaving Bane to rebuild the team.
Eventually the main group reunited, and even managed to rescue Knockout from Hell, so the final lineup for the Secret Six was:
Yes, there were eight of them. Who cares? The team is awesome, and hopefully they'll come back some day, on the other side of the DC reboot. And while you can't build any one complete version of the team, there are currently at least six toys of various Secret Six members. But still, we need to see some more. We need a super-articulated Ragdoll (ie, more articulation than even Deadman), a nice Scandal, a Knockout who's not short like Little Barda was and a King Shark BAF. Make it happen, Mattel!
*King Shark had an action figure in
Kenner's Hasbro's Man of Steel Total Justice DC Super Heroes line, but that was in a 5" scale, and is thus unsuitable for mingling with modern figures. Also, he is a shark.