1955-1959: Ice Capades The original Chip and Dale costumes from 1955, which like the majority of costumes, were borrowed by Disney for the opening of Disneyland
1960-1968: In the 1960s, they looked identical, with no character distinctions.
1968-1982: The 1970s Chip and Dale costumes had larger eyes and larger heads with extra neck fabric.
1982-Present: Modern Chip and Dale. The current Chip and Dale costumes, seen since the early 1980's get new smaller heads and ditch the extra neck fabric. They've also been given distinct characteristics. Their hands are now four-fingered.
2008-present: The articulated versions of Chip and Dale, seen in various live shows. Notice that Dale has a hairpiece on the top just like his animated version. They also are slightly shaggier.