I have found that you don't need a ton of tools to work with ice and break it down. An ice pick certainly. And an ice chipper will make life much, much easier. Cocktail Kingdom has some nice picks and chippers here. Up until recently I used a pick to break blocks down into large cubes and then a chipper to roughly shape them. Sometimes I'll also use a large chef's knife when making spheres but the potential for injury seemed pretty high on that one so I ran a file over the length of the blade to blunt it a bit. I'm sure that's cheating in some circles but it still works fine.

The tool which I knew nothing about though is the slag hammer. This thing is awesome and has quickly become invaluable to me when breaking down ice blocks. Sean has some background in metal smithing and was familiar with the slag hammer. Apparently it was used to chip off the oxidized material surrounding a weld joint. It has two ends that T off of the handle. One looks like a miniature hatchet and the other comes to a point. Neither end was sharp. At all. And the first time I used it on ice it didn't go so well. However, once I put it on a belt sander and got a nice edge on the hatchet side...well, I hardly ever use the ice pick now. The slag hammer has just the right amount of weight to break things down cleanly and efficiently. And, as an added bonus, you can find them at flea markets and antique stores, usually for less than $10.

The technique I use for breaking things down came from Alcademics and involves using a pick to score/chip a slight channel where you want the ice to break and then increasing the force used and focusing on the center. The slag hammer doesn't mess around here. The channel develops quickly and after a few heavier taps near the middle the ice breaks apart nicely.