When constructing an initial mock up of screens for a web application, what tools would be best to use? For starters, I'd like to avoid MS Paint and MS Visio!
Ideally I'd like ones that:
There is a trial version, but if your project is open source you can get a free version or if you match any of the other criteria (see bottom of the page).
It is a very nice tool, that makes nice looking mock designs. The rough and "hand drawn" look means they are only useful for mocking up designs, but this is a plus - people are more likely to change them or throw them away. It also includes a load of templates and other common UI tools to speed up the design process.
You can also take a look at our ForeUI, we also give away license to blogger/reviewers.
ForeUI can create both static and clickable mockups for web site.
I am really liking Mockingbird and it is free.
You can create projects then just send them an email to view the mock-ups. No need for an account to view mock-ups. So anybody can view your project.
EDIT:
Mockingbird is no longer free. Still a great service if it is frequently used.