I keep seeing books on this site, maybe you should check that out. It is on the left hand bottom of this page. I believe it's from amazon.com. Good Luck!
Basically, the major cake decorating techniques are
1. baked-in/on decoration - fruits/nuts etc that are placed on the batter before cooking eg almonds on fruitcakes, struesal on coffee-cakes, glacee/glazed fruits on the bottom/top of cakes, marzipan on battenberg/simnel cakes etc
2. simple decorations using glazes and sprinkled powder patterns [icing sugar, cocoa etc]
3. slathered/piped whipped cream
4. Marzipan
5. Marzipan and Royal Icing [most have a variation of this technique - Special mention: English Lambeth technique]
5. Marzipan and Sugarpaste [Variations: English, Australian, Indian, South African, West Indian Methods] Sugarpaste = Rolled Fondant
6. Buttercream [most cultures have a variation of this: Swiss, French, German, Italian, American, European, English to name a few] Wilton is an exponent of originally Buttercream then Rolled fondant
7. [Poured] Fondant - usually for small dainties like Petit Fours, but can be used on small larger cakes eg 2" 4" 6" but not usual.
8. Satin[Silk] Icing is a buttercream variation [most have a variation of this technique]
9. Rolled Buttercream [Fondant] is a buttercream variation
10. Marshmallow Fondant is a unique and recent developement
11. Chocolate techniques - straight melted chocolate, ganache, chocolate clay [candy clay] etc
12. Icings and frostings [sky's the limit and everyone has their own recipes]
I do not think I have left any out....
I have read the Toba Garrett book. The Australian Method she is referring to is Rolled fondant Cake-Covering, Sugarpate/gumpaste/pastillage decoration with piped Royal Icing decorations like Extension-work [US term - string work] Flood-work [US term - run-outs] etc
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