Recommended by Yuuk-chan
"FARTHER" and "FURTHER"
"Farther" refers to physical distance. "Further" relates to metaphorical or non-physical distance. Ex.: The park is farther than I thought. We need to look further into this issue.
"WEATHER" and "WHETHER"
"Weather" refers to the atmospheric conditions. "Whether" is used to introduce alternatives or choices. Ex.: The weather is perfect for a picnic. I'm not sure whether to wear a jacket or not.