Cohesive colors is a color palette randomizer that does a great job picking a set of 5 colors that work really well together, and also allows you to throw a hue adjustment on them all.

This would be good for a quick way to colorize game levels or websites to make them look distinctive without too much effort.

For websites, I like to come up with a set of base colors, assign them to variables, and then lighten them to various degrees to use in different contexts.