Crazybump is probably pretty well known to other modders, but I recently discovered this extremely powerful tool.
http://www.crazybump.com/
I highly recommend trying this out for anyone in modeling; it's very easy to use, and easy to understand. It has a previewer that allows you to see your changes in real time. I highly recommend this awesome tool, it's just amazing.
I have been using it since summer. A really great tool indeed!

Ohhh that seem like a nice tool!
yhee... gife to Linux and Mac =)
I'm sorry, the video won't load for me, and I can't get any information from the website... what is it exactly?
Basically, you give it a texture, and it creates a Normal(bump), Disortion, Spec, Diffuse, (and one other I can't remember)
For each texture it creates, you have about 3-5 sliders that changes how strong or detailed the new texture is.
One of the best features is it gives you a light-weight Model Viewer that uses all the textures it created. When you make a change to a texture, it updates also; This is a really cool feature.
Saving it is easy; when you save it, it creates a new file for each texture, which are named like each other; I highly recommend this for anyone who creates textures for games/modeling.
Basically, you give it a texture, and it creates a Normal(bump), Disortion, Spec, Diffuse, (and one other I can't remember)
For each texture it creates, you have about 3-5 sliders that changes how strong or detailed the new texture is.
One of the best features is it gives you a light-weight Model Viewer that uses all the textures it created. When you make a change to a texture, it updates also; This is a really cool feature.
Saving it is easy; when you save it, it creates a new file for each texture, which are named like each other; I highly recommend this for anyone who creates textures for games/modeling.
Oh wow that is amazing... thanks for telling me 
Crazybump is sooooo old its a clasic

i use it everytime i need a bumpmap (well when my app doesent make a decent one XD)