Are you talking "new" or used? Must they be current or recent production?
My simple answer is usually the JBL L7. They're a 4-way with a very powerful 12-inch side-firing woofer that plays better than most 15-inchers. I know what they're capable of because I have two pair and my main system has these 18-inch 4-ways to compare them to (you did say "big bass" right?).
That's a 4-inch voice-coil under that dust-dome and the little mid-bass is a 10", just to give you a sense of scale: