Other than all the obvious ones, I consider Tramadol Instant Release to be an "extended release" medication, since the tramadol is slowly converted in to the powerful O-Desmethyltramadol over several hours. It gives me a solid 9-12 hours of analgesia once the O-Des starts kicking in at the 2 hour mark.
The only problem is that your unique level of CYP2D6 enzymes in your liver determines how much is converted. It works great for me, as I have multiple copies of that enzyme. People with regular amounts find tramadol a weak opioid, and ones with CYP2D6 deficiency find it useless.