A wireframe is an early design that can help you and your team get agreement about what the design should look like and how it should behave. This is similar to how an architect may create a sketch of a building or how a director may create a pencil storyboard of a movie. The purpose of the wireframe isn't to have a completed product it's to get high-level agreement on the overall flow.
There are many specialized tools to create wireframes but I believe that many of these actually get in the way of the creative process. The most common problem is that they often render visuals that could be confused for an actual design. This can make people think that they are looking at a specification and they will critique the minor points and word-smith instead of engaging in a discussion about the high-level work-flow.
The other problem with highly specialized tools is that they tend to make the designer behave like a programmer wiring up pages with links and actions. The wireframe is not meant to be a working prototype. It's meant to be fluid presentation of the high level application structure.
I often wireframe using a pencil, a ruler and a stack of paper:
Paper has the property that you can do anything you want. You don't need to find a checkbox in a dialog you simply draw a checkbox. You don't need to wire-up events you just draw what you want it to look like.
The advantage of wireframing in pencil is that the design is obviously not complete and it gives you and others creative freedom to try things out and move things around.
I took the same principal and applied it to a Powerpoint template. All the parts can be easily moved around and customized. The parts have a pencil drawn appearance. Making it easy to edit, customize and add.
It's not as flexible as paper & pencil but it does make it easier to get executives and developers to edit a wireframe and explore UI concepts and ideas.
This sample includes a number of sample screens showing how various web-page parts and techniques can be mocked up.