What to do with a Sizzler?
My version of this ( http://www.amazon.com/Lodge-Logic-Pre-Seasoned-Fajita-Set/dp/B00008GKDP/ ) actually came with a set of instructions. It's not meant to be used for cooking, only for serving. Place the pan in a hot oven for about 30 mins to heat it up (while you're cooking), then put your fajitas on it to bring to the table. The cast iron will retain heat for a long time and keep anything you serve on it sizzling hot.

A cast iron pan would be a great way to cook fajitas, but the shallow sides and strange shape of the "sizzler" pan make it impractical to really cook on. The same instruction book also recommends using another cast iron pan (two, actually) to cook the fajitas.

If you want to use it for something other than fajitas, it would work just fine as a small griddle. You could probably cook pancakes, a strip steak, or chicken breast on it, but nothing that requires any stirring.