How to make large clear ice cubes
Wired Magazine had a recent guide on how to make crystal clear ice. I'm copying it here since the article says it's under Creative Commons license:

Go Big
Ditch the ice tray and use a large vessel like a thick plastic bowl or, better yet, an insulated cooler. Fill it with water and stow it in the freezer. 

Wait
The H2O can take a day or so to solidify. Remove the mini berg when it’s solid on the outside but still has a liquid core. 

Drain
With an ice pick, bread knife, or screwdriver, make a hole to release the trapped water. 

Segment
Score a grid onto the slab of ice, then pry it apart into cubes - the ice should break cleanly along the seams. Bigger cubes are ideal because they melt more slowly. 

Contributed by Camper English