My favorite wive's tale is that if you see a turtle crossing the road it will rain within 3-4 days. It's really true, at least most of the time. Last week I saw a turtle crossing our county road, but I think he was just looking for water as all of our stock tanks are drying up and we have no chance of rain in the forecast.
Another saying my mother always used was if you see a ring around the moon, it will rain soon. She also said that "sun dogs" (those glowing orange spots to one or both sides of the sun late in the afternoon) were a sign of rain coming soon.