Hair ties and ink pens that work are the two big things around here that always seem to go missing. I can find them all day if they aren't actually needed right then.
Ha ha... hair ties here too. I can never find sharp knives in my kitchen. I swear someone is stealing them! I complain about it and the next day they are in the dishwasher.
Matching socks for the kids. I finally started buying them all black socks. Now my problem is finding matching gloves. I can find one glove, but not its mate.