my dog loves Bully Sticks. I usually buy the ones made by Red Barn. Here's a link:
http://www.redbarninc.com/c-11-bully-sticks.aspx
I only buy the 12" or larger variety. As soon as the stick is chewed down to about 3", I throw it out.
another long lasting one is a filled hoof, by the same company.
warning - these stink!!!