I am relatively new to ABAP and I can say that for me, at least, this is an invaluable guide to the language. It covers commands up to release 4.6 but it is not clear whether this is 4.6c or 4.6d or some other release.
It lists all commands alphabetically which is a shame as I thought they ought to have been grouped by subject area (e.g. string functions, maths functions etc). However if you have a rough idea what you are trying to do, you should be able to find the command you need.
The appendices list the system tables, transaction codes and other useful information such as type conversions and how to do batch data communication.
A very useful book for the beginner in ABAP and, I suspect, the seasoned pro as well.