We had this the other night - it didn't have enough raspberry flavor, so I think I'll try doing a cherry next time with grenadine. It was really good, though.
1 (12 oz) can frozen limeade concentrate
1 (2 ltr) bottle Sprite
That's it! Crazy, huh? You can just add the raspberries for garnish if you want. If you want it like Red Robin, just add a bit of cherry grenadine into the bottom of each glass and then pour the limeade into it. Or you can pour the juice of 1 10oz jar of maraschino cherries into the entire thing.