Mom, I'll hate her if you want me to.
-- Ben Harrison
It's easy to find movies about evil stepmothers. Far rarer is a realistic (and still entertaining) treatment of the modern "other mom" situation, which often proves problematic.
In this 1998 film, Ed Harris is dad, Susan Sarandon is mom and Julia Roberts is in the awkward position of stepmom to two kids. It's full of conflict and truth and some very poignant moments as the family works through this common post-divorce, modern family makeup.