Hooking off the jab is my favorite combination in boxing. It is incredibly hard for the other guy to block if you do it right. Typically the other guy will try to circle away from your right hand (rather than slipping left), and will haplessly take the hook. Then you finish with the right cross/left hook to body.
The key is getting the hook off the jab right, and that requires footwork. You throw the jab and then step into it as you pull the arm back, loading your hips, meeting your arm coming back like halfway, and pulling your rear foot in.
The guy who does this most right now is Wlad Klitschko. Watch his fight v. Castillo to see him doing it beautifully. It's unblockable if you have already established your jab -- that hook crashes through over and over again, because it looks exactly like a double jab.
Make sure you establish your jab first before trying it tho, lest you catch a straight right/jab counter.