I like this one
Ingredients:
1 large Onion
1/2 cup Soy Sauce (low salt kind)
1/8 cup worchester
2 large Garlic Cloves
Directions:
Cut onion into quarters Cut garlic into quarters. Blenderize all ingredients until liquefied.
Marinate for at least 1 day (2 days are better)
I've also tried making a marinade and after combining with the meat, put everything inside a zip lock bag and freeze it for a few weeks.
Seems to help tenderize the cheaper cuts of meat.