Thanks fh, you must have caught me on a good day.
The most useful resource I have found is the online help. There are lots of examples of code to use in formulas, as well as it is the best way to keep current with all the new functions that are continually added.
However, for new users, the dummies book is pretty good, and the differences between 7 and 8 aren't that great at the introductory level. Haven't read the others though.
If you are using ODBC/SQL, you should also plan on learning some SQL after you've got a handle on CR.