I use a couple variations;
1) an Italian salad dressing from a company called Chiavettas. As far as I know this is only available in upstate NY (my mom brings us several bottles every time she visits).
2) A mixture of bourbon or whiskey, steak sauce, garlic, salt and rosemary (Note: do not use husband's Single Malt; he will not be amused)
3) Fresh cracked peppercorns, red wine vinegar, course-grain mustard and a bit of olive oil. Simple and yums.
Sometimes I'll also use a bit of ginger in a terriyaki-type sauce, which is o.k. as a steak but really great when the leftover meat is combined with soba noodles the next day.