Blue Coins first appeared in Super Mario 64, and were worth five Gold Coins each. There are also Blue Coin Blocks; when Mario attempts to Ground Pound on them, the Blue Coins appear near to Mario as the time starts. They return in Super Mario 64 DS.
In Super Mario Sunshine, ten Blue Coins can be exchanged for one Shine Sprite. There were 240 Blue Coins in the game, so a total of 24 Shine Sprites could be exchanged for Blue Coins. In Mario Pinball Land, these coins can be obtained by making a combo without using the flipper. Mario can use them to play mini-games from Toad for Power Stars.
The blue Coins found in Wario Land II (called 100 Gold Coins) are a special kind of coin Wario can collect that awards him 100 Gold Coins.