There are a lot of tools out there. Here's a page full of options for you.
I have used Balsamiq and am currently collaborating with a team that uses it. The trouble I have with it and some other wireframe tools is that they are so ugly (in an effort to communicate "not ready") that it's just distracting and sometimes hard to communicate with.
Coming at the problem with a creative background, here's my solution. I keep a "default UI kit" on hand with all the user interface elements I've built up over time. I work mostly in Illustrator but you can do the same for Fireworks or Photoshop. Then just do your work with the UI kit on one screen and the wires on the other. We often build out our initial wires in a brainstorm session so the kit is on my laptop and the mock-up is on the presentation screen.
That workflow also allows you to do a little customization for unique dashboard requirements like temperature meters or dials or custom timeline implementations. It's less restrictive but, you do have to reign yourself in if you want to stay on task with just outlining ;)