How to point domain name to another hosting provider?

We're currently using our domain name for email only. We want to link the domain to a hosting provider we're using for our company web site. I've changed the A names to point to the correct IP address, I've changed the name servers to point to the correct host. It's been over 24 hours now and the changes still have no propgated through DNS. I know DNS can take up to 24 hours to change but the UP TO 24 hours is extremely, extremely rare, usually it's 10 - 12 hours at most.  What else do I have to do to make the changes take?