Algorithm to implement a word cloud like Wordle

Question

I'm the creator of Wordle. Here's how Wordle actually works:

Count the words, throw away boring words, and sort by the count, descending. Keep the top N words for some N. Assign each word a font size proportional to its count. Generate a Java2D Shape for each word, using the Java2D API.

Each word "wants" to be somewhere, such as "at some random x position in the vertical center". In decreasing order of frequency, do this for each word:

place the word where it wants to be
while it intersects any of the previously placed words
    move it one step along an ever-increasing spiral

That's it. The hard part is in doing the intersection-testing efficiently, for which I use last-hit caching, hierarchical bounding boxes, and a quadtree spatial index (all of which are things you can learn more about with some diligent googling).

Edit: As Reto Aebersold pointed out, there's now a book chapter, freely available, that covers this same territory: Beautiful Visualization, Chapter 3: Wordle

Here's a really nice javascript one from Jason Davies that uses d3. You can even use webfonts with it.

Demo: http://www.jasondavies.com/wordcloud/

Github: https://github.com/jasondavies/d3-cloud

I've implemented an algorithm as described by Jonathan Feinberg using python to create a tag cloud. It is far away from the beautiful clouds of wordle.net but it gives you an idea how it could be done.

You can find the project here.

I've created a Silverlight component that uses the algorithm Jonathan suggests here. The source code and example projects are all available on my blog:

http://whydoidoit.com

My cloud lets you color and size words based on different weightings and it supports word selection (from a coordinate) and selected word highlighting. The source is yours to use as you see fit.

I'm working on WordCram, a Processing library for making word clouds. It's pretty heavily influenced by Wordle, and is informed by the same PDF aeby linked to above. It handles the collision detection for you, and lets you focus on how you want your words laid out, colored, rotated, etc.

http://code.google.com/apis/visualization/documentation/gallery.html

Check out the word cloud visualization. Not as fancy as wordle.net but real easy to add to your site.