Walt White is Hal from Malcolm in the Middle (which is funny, considering that Malcolm... had one episode where Hal worries that he may have cancer, another where Hal is busted on drug charges, and a flashback where Hal is bald from a chemistry kit accident), if he left his wife and kids and took several levels in Badass.
The leader in Jesse's addiction recovery group is an Expy of Tobias Beecher. They both suffered from debilitating addictions that ended with an innocent girl run over by a car. Also, he's Justified's resident nutjob, Mr. Wynn Duffy!
Another Justified regular is Tucker's friend - who is also resident idiot Dewey Crowe on that show.
Apparently Cranston had specifically taken the role because it was so different from both Hal and every other bumbling dad role he'd been offered around the time. Read that how you will.
What Could Have Been: Learn anything about the issues this show has faced that caused radical plot rewrites, and marvel that it turned out so well. For starters, if the first season hadn't been cut short by the writers' strike, Jesse would have been killed at the end of it.
Also, Vince Gilligan originally envisioned the show as being only four seasons long. Its possible that the actor playing Tuco deciding to leave earlier than expected made the writers have to build up to a new villain thus making the story longer than originally planned.
Hector Salamanca was originally planned as the villain for Season 3, and Gus Fring would never have existed if Tuco's actor hadn't resigned.