In an entertaining Interview with Cameron Adams (the Man in Blue) last month, he talks about the difficulty of creating a Scrabble game using CSS and JavaScript:

The HTML code and visual design were fairly trivial to come up with. (Scrabble isn't exactly the best looking board game to hit the shelves) It was the behaviour layer — the JavaScript — that was the hardest part.

Of course, upon reading this, I had to check out the Scrabble game. Here it is. It's a solitaire Scrabble game, but other than that limitation it's quite well done. Read more about the game, and if you're really obsessed you can download a version with a much larger dictionary of words from that page. The game is written in standard XHTML / CSS / JavaScript and works fine for me on Firefox and Internet Explorer 6.

Here's a link to the source code if you're curious. There's some complex code in there for checking the various possibilities of gameplay. One nifty trick: the dictionary is stored in a compressed format and uncompressed by the JavaScript code when the page loads.