This is a dual alignment laser for the Chinese laser cutters. This uses the really small (and cheap) 6mm laser pointer modules, which you can get for under $1 on ebay, DX, etc.
The laser cutter I purchased already had a laser pointer, but just a single one attached to the side of the head, which only points at the correct cutting spot at one point. Some people have made attachments that use two laser lines at 90 degree angles to each other, which always has the crosshair aligned with the cutter... but the biggest problem I had was making sure the object I was working with was at the correct height, so the cut/engraving was properly focused. So I decided to use two laser dot modules, which, when overlapped, will tell you that the object is at the optimal distance, and will point to the spot that the laser will cut (I don't really care where the laser is going to hit unless it's properly focused).
I designed the part in two pieces, which lets you individually slide the laser pointers around in all directions, so you can get the alignment set perfectly. The laser dot modules are slightly focusable, by turning the tip of the brass module... they usually have a small bit of glue that you need to break. I tried to adjust the focus to be nearly correct, though I also put just a small hole in the tip of the laser holder, which helps to cut down the size of the laser spot.
Attached are the STL files, as well as the Sketchup design files. You can see this mod, as well the rest of my CO2 laser cutter setup @ http://www.projectvb.com/laser_cutter/ .
-print two laser holders
-(optionally) adjust the laser pointer focus by twisting the tip of the module
-press the laser modules into the laser holders
-(optionally) add caulk or some other opaque material to block light from coming out the back of the laser module.
-print both laser alignment pieces
-attach the laser holders to the alignment pieces with #2 screws (I think I used 1" long, which was a bit longer than needed)
-attach the assembly to the laser cutter. I mounted mine to the existing holes from the single laser pointer, using the original #4 screws. It may require a couple modifications if your laser cutter didn't come with the holes for the laser pointer.
-wire the laser pointers
I cut the wire to the existing laser pointer, and wired the new ones into it (it ran on 5V, so you need to make sure to get the appropriate laser module for the voltage that you'll be running it at). I added a switch, so I could turn it off (staring at the red dot can get annoying some times). I heat-shrinked the wires to keep it tidy, but that's completely optional.
-align the laser pointers
It takes a few minutes to do, but basically you want to take something like a piece of painted wood, set the laser to low power, and momentarily press the test button, then move the object closer, press the test button again, etc... until you can determine the optimal focus point (where the burn dot on the object is the smallest). Then, leave the object and laser head locked in place, and point both laser pointers overlapped at the burn spot on the object, and tighten down all the screws.