A light sprinkling of either sea salt or seasoned salt and cracked black pepper makes for the perfect ribeye IMHO. I've used a few marinades that have worked out well but simple seasoning is always what I come back to for a good steak.
It's not really grilling, but ever try garlic butter and parsley as a final saute for your steak? A few seconds based either side in that mixture makes a steak, beef or pork, delicious.
Yeah garlic butter rocks, even normal butter does. I make a braised pork cheeks dish where I seal the cheeks in oil, then add a knob of butter for the last 30 secs of sealing and it makes a world of difference.