What Camera Speedlights (flashes) in the market that can be fired using another flash?

I haVe a Nikon D80, and a Nikon SB-910 speedlight. I have a Phottix Strato II Flash trigger.

I was wondering, since I started to love strobist works, my Phottix Starto II are a set of Receiver and Transmitter only. And what if I want to add another flash to my strobist work, I was wondering what flashes in the photography market (even if not Nikon) that will trigger in sync just buy my SB-910 on my Phottix Strato II. I can't buy a new set of Phottix Strato II because they arent trans-receivers, again, its a Receiver and Transmitter only.

Note: I can't use Nikon CLS, because my pop-up flash is broken.

The 420EX, 430EX, 550EX, 580EX can all be slave units.
For remote actuation the master has to be a 550EX, 580EX or ST-E2. - and therein lies your problem because they will not work on your Nikon D80.

Since you are talking about using optical slaves, any flash on the market can be set off this way. You just need a simple optical slave for each flash. They are cheap, and require no batteries or moving parts. The simplest ones are a small hotshoe, just like the receiver side of your radio triggers.

Optical triggers have a few down sides… Any flash fired will set them off, and they have limited range outdoors in sunlight.

The easiest way to solve your problem is to purchase more receivers for your radio trigger. That solves the range problem, and the problem with other photographers setting off your flash units. And, they will work with any flash on the market. You don't need $500 Nikon units, you can buy $40 Yongnuo flashes and they will work just as well.

I own two such flash units from Ritz camera. They're tripod mountable and use AAA batteries. They work very well as optical flash units and I trigger them with my on-board flash. They're running, I believe, about $40 each.