Jasc Paint Shop Pro has this filter called "Clarify" which does a great job of removing haze from pictures. The description it gives is:

"Use the Clarify command to give your images a crisp, focused look so objects stand out. This command adds a sense of depth and clarity to the image. It can make hazy, foggy, or slightly out of focus images look clearer."

I should emphasize that the effect is very different from sharpening.

What is the closest equivalent in Photoshop?

[Edited 2007-12-31 00:21:59]