We've just stumpled onto a product, Liquid Calcium by Blue Bonnet, that is supposed to be 85% absorbable. But when we take it, we can feel it's soothing effects. www.drwallach.com has some colloidal calcium for $37 that is supposed to be 98% absorable--but Blue Bonnet was only 8.79--big difference in price.
I've heard Bearfoot's Coral Calcium makes him laugh all the way to the bank.