Strong female character example: Cordelia Chase from Buffy The Vampire Slayer. She's definitely got a mind of her own, doesn't lose herself to any guys (which is why I passed up Buffy herself in this example, she definitely acted a lot weaker and more helpless when she was involved with Angel), and isn't afraid to say what's on her mind or stand up for herself (and others, occasionally). She has her flaws (such as being rude and catty and selfish, especially when she was on Buffy), but she learns from her experiences and changes for the better.

Weak female character example: Two of the three leads from Charmed-Piper and Phoebe. When Piper was having problems with her boyfriend/husband, she was virtually useless and miserable and either completely refused to help innocents or whined incessantly about it. She was all about how annoying innocent people were by getting killed by demons and warlocks and how it interfered with HER life. Phoebe's main focus in the last four seasons was finding a guy and having said guy knock her up. At one point in the last season, Phoebe was perfectly fine getting married and starting a family while under disguise as her cousin. Wanting to get married and have kids does not make a weak female character in itself, but that's literally all that was driving Phoebe. These characters got more and more unlikable and selfish with each season, and the amount of people they actually helped diminished too. All too often they were willing to put aside potentially cataclysmic situations for dates. It was pretty rough.