What type of flash/diffuser was used in this picture ? I am amazed of the by level of diffused light. I am sure there is a lot of post processing but i believe the lighting is the most important aspect.
It actually says in the description: "lighting- extern flash canon 480II+ difuzor"
I guess he either used the diffuser supplied with his speedlite or, as Matt above mentioned, a Sto-fen diffuser (these are the most popular nowadays).
Yes you are right, light in macro photography is really important. I'm surprised that he managed to achieve such excellent light diffusion with his speedlight instead of using the o-ring flash attached to the front of the lens.
When it comes to diffusion and soft lighting, it is the relative size of the lightsource that counts. Even the smallest diffuser such as one of those Stofen thingies will act like a huge softbox, when your subject is the size of an ant!
This was was produced with a bare speedlight i.e. no diffuser at all:
In another image here, you can see in the droplets that he probably used some kind of a (round?) diffuser on the flash unit. There is no evidence for side reflectors or other modifiers.