If you're in the market for a new death ray, an important thing to consider is what you'll be able to do with it when you're not busy committing nefarious acts. One option is coffee roasting, and, if you're so inclined, you can even contribute to an open source project that's looking to create a giant mirror array capable of superheating air to 2,000 degrees.
Solar Roast Coffee has a long and noble history of using progressively larger and more complicated solar concentrators to brown its beans in an eco-friendly (and apparently very tasty) way. A solar concentrator is basically just a big pile o' mirrors that cooperate to focus sunlight on the same spot, and if you use enough mirrors you can generate massive amounts of energy.
For its latest project, Solar Roast wants to construct a bigger, better, and more versatile solar concentrator that can be used for just about anything, and the group is open sourcing the whole thing and going through Kickstarter to make it happen. The final product will be a prototype system along with detailed plans on how to make your own, which on a sunny day will be able to produce up to 1,000 kilowatts of heat energy that can be used for roasting or melting anything you feel like roasting or melting. Just try not to point it in my direction, please. I burn easily.