The only marinade I've ever bought are those little packets of Adolphs Meat Marinade that you mix with water. I used to use them to marinate sirloin tip steaks so they'd be tender enough to grill. Last time I bought it, I found it awfully salty, though. I think my tastes have changed.
I usually either use Italian dressing or make my own marinade any more. In so far as steak is concerned, we now buy whole ribeyes, and Kim cuts them into steaks. They don't need to be marinated to be tender.
We get by with a little help from our friends