So many answers to this - Do you know what direction or flowers you would like to start with?
There's Designmecake like kazita recommends but there's many others depending on where you want to start.
There's Sensational Flowers1 (roses) & 2 (orchid) by Jennifer Dontz (sugardelights,com)
SugarEd Productions has several
Craftsy.com. - Exotic Orchids by James Roselle and in Fondant Frills by Maggie Austin, her cabbage rose as well as Jacqueline Butler's Handcrafted Sugar Flowers
CakesbyDesign by Scott Clark Woolley.
I have many from the above list - I use them all and refer back to them when needed. If nothing else you now have some places to explore :)