Best software/plug-ins for creating web UI designs?

There's no magic involved. It's all hand built using applications like Photoshop and Illustrator.

 

Fireworks is a little more tuned for this sort of thing than Photoshop.

'manual' example: There really isn't a 'make it look good' button.

 

Sophisticated design doesn't come out of a box.

Could you likewise ask what musical software is best for writing a good song?

It's the melody in your head that makes a good song. Like wise it's the aesthetics you possess that make for good design.

The program merely allows you to put it on the web.

 

Great analogy, citizenzen.