What is a good tool to design the implementation of websites? I typically use UMl to design applications, but I feel that does not apply well to websites, specifically the heavy emphasis on UI that websites require.
What would be a good tool to use to plan a webpage?
Well, I use PowerPoint to create web page mockups. It's fast, and allows you to create "storyboards" that simulate actual use of the website and its various pages.
PowerPoint is great for presenting conceptual ideas, or modeling the UI for a real person to see if they understand it (kind of like a high-resolution paper prototype).
The PowerPoint Prototyping Toolkit provides a collection of shapes, such as textboxes and dropdowns, that assist in creating form mockups. This template is also useful.
For the UI, I'd certainly not use UML but a wireframing tool like MockingBird or Pencil. The first one has my preference, it's awesome. Just try it.
What kind of model do you need?
Are you capturing some information about the visual aspects? In which case wire-frames or other story-boarding techniques are good.
You also need may to capture navigation information, which can be done via story-boarding but sometimes a UML state diagram is more succint and easy to reason about.
Then you may also wish to capture the data model associated with each state, and in which case a simple UML class diagram works well.
In an AJAX-based app you also need to document the "invisible" ajax activities, and again UML state diagrams along with classes for the invoked REST services can be helpful.
You can take a look at ForeUI. You can design not only the UI but also the behavior of the website. Here is an example: Blog Mockup Created with ForeUI