A great cardigan sweater is a key piece of any wardrobe. While sweaters are typically winter wear, a classic cardigan works year round, keeping you warm when the office a/c is turned up too high or draped over your shoulders at the end of a cool summer night. Once the appurtenance of preppy scholars and librarians, today's cardigan sweaters remain classic pieces that can be adapted to all the best trends. We’ve put together a list of the trendiest cardigan looks worn by your favorite celebrities. For each designer piece, we’ve found a more affordable alternative that looks just as the higher-priced original.