I admit that I'm typically a purist and just go with salt if anything. However, I frequently use Montreal Steak Seasoning and I also use a soak I got from a guy on another forum. It's simple.
2 Tbsp Olive oil
1 Tbsp Soy Sauce
2 Tsp Montreal Seasoning
1 Tsp Espresso coffee
Tastes great on smoky, grilled stuff.