How do you explore early UI ideas? (pen and paper, whiteboards, Balsamiq...)

Why have your chosen this technique instead any other alternative?

Thanks for your answers!

Starting mostly with some research in the field (web search). Drawing some fast sketches with a pen and paper. To get interaction in the GUI and presentable to clientsI use Mockflow for wireframing. After that I mostly design with Photoshop.

I like to hear some tips about getting more pages dan without copying all the layers to a new folder or file in PSD.

Thanks, Marcel @ userflow