What's the standard paper about optimisations and program transformation?

A recent one is "Secrets of the GHC inliner", available here: http://www.research.microsoft.com/~simonpj/Papers/inlining/index.htm The other good place to look is Andre Santos's thesis (sorry, I don't have a URL for that handy).

Which transformations are used by the GHC, especially which optimisations are applied at optimisation level 0, 1 and 2?

The only transformation which is currently applied at level 2 but not level 1 is constructor specialisation (it is experimental and we haven't measured the benefit yet). Level 1 has everything else turned on, and level 0 has simplification only. Cheers, Simon