I've recently had some spare time to start writing training notes for a Oracle SQL Developer course here in Australia for my company SAGE Computing Services. While SQL Developer in its infancy contained few features compared to Quest's Toad, today as new revisions come along it's developing quite a varied set of features that are making it a tool of choice for many sites (not to mention it's free).
In writing the training material I've collated all SQL Developer's hotkeys into one document which I share with you here. You can of course determine these for yourself by visiting the Tools -> Preferences -> Accelerator menu options, but this collated document should save you the hassle of reading through all the different options.
Happy SQL Developer-ing!