Ellen and Jo Harvelle, <em>Supernatural</em>
Supernatural's attitude toward female characters is… um… problematic. Basically, they all get killed. If a female character is introduced, you can be damn sure she's going to hang around long enough to forge some sort of emotional connection to one or both of the protagonist Winchester brothers before either A) being written off the show in a way that makes no damn sense (see: Anna) or, more likely, B) dying in some gruesome way, as is the case with Ellen and Jo Harvelle.
(I should note here that last season saw Bobby and Castiel, the show's most longstanding male secondary characters, get killed off as well… but that's season seven. And we don't talk about season seven.)
Ellen (Samantha Ferris), the show's matriarch figure, ran hunter gathering spot the Roadhouse before it was unceremoniously burned to the ground in season two. She subsequently gets back into hunting, though she’s not too keen on her daughter Jo (Alona Tal) following in her footsteps. What's so great about the Harvelles is that, in the midst of all the never-ending Winchester family drama, Ellen and Jo had a positive, realistic mother-daughter relationship. Sure, they fought—as a headstrong mother and her headstrong daughter are going to do—but you knew they'd always do the right thing by each other.
Which is what makes their death in season five—Jo is mortally wounded, and Ellen stays by her daughter's side to trigger the explosion that gives the Winchesters a chance to escape—all the more heartbreaking. Theirs was one of the only healthy family relationships in the show (say what you want about Sam and Dean, their relationship is way too codependent); losing the Harvelles was not only one of the most gutwrenching moments in a show all too full of them, it also deprived future seasons of a pair of awesome ladies who could be depended upon to take the Winchesters down a peg or two when needed.