Siemens actually publish a very good series of books (yes they do!) by Hans Berger which cover all aspects of S7 programming in LAD, STL, SCL etc. All the mysteries of indirect addressing, pointers, address registers are covered and each book has a disk with example software.
The best one for STL is "Automating with STEP7 in STL and SCL". The copy I have has a Siemens order number on it of "A19100-L531-B819-X-7600" - what a part number for a book!
regards
Ken.