Wireframing tools for web design

Hey everyone,

I am a junior designer at an established web software company. I am surprised to hear they use Excel for the majority of their wireframing during the design process. I am primarily an algorithm designer, but I am frequently involved in the layout and user experience process because I communicate the technical requirements to the design team and occasionally make my own designs.

Can anyone recommend a good alternative to Excel for wireframing? I am a programmer by nature, and can write javascript and html, but I want to be agile to anticipate the rapidly changing design process.

Thanks.