I just generated specular, displacement and normal maps for a diffuse texture using CrazyBump and i would like to know which shader in Unity allows me to use all of those maps together. I’m just able to find shaders with either bump mapping (normal), or specular. 
there is no shader that supports displacement.
Generally they don’t make much sense for realtime anyway as the idea of shaders in this case is to fake detail but displacement require the geometry to be present to displace it
Actually when speaking displacement in realtime shaders we are really speaking about either paralax or relief mapping. 
and those techniques do make sense in realtime application’s on the newer hardware(eg. ‘next-gen games’). 
Armagon, I’m new to unity(running trial) so I haven’t yet browsed the shaders,
but if there isn’t a paralax or relief ennabled shader in untiy,
then perhaps deepening your normal-maps is a good option?
here’s a tutorial that should give you a clue as to how go about it in PS,
or you could just use crazy bump:
http://www.cgtextures.com/content.php?action=tutorial&name=normalmap
There is a group of built-in parallax-mapped shaders, but no relief mapping shaders.
I would advise against using the linked method on your normal maps. I honestly don’t think the author understands what normal maps are, and the results of his process look like the surface has been bloated rather than just scaled.
Normal maps can and should be generated directly from height maps (not from diffuse textures as the guy in that link does). To make them appear deeper, any decent normal map generation utility should give you a scale factor that defines how the height information is to be interpreted.
All that said, parallax mapping (or steep parallax mapping, if you want to find or make a shader that does it) is probably the best solution for giving surface detail more depth.
Indeed, I agree that creating a Heightmap from the diffuse isn’t as simple as just converting the image to 16 bits per channel and de-saturating it, but the method of deepening the normal maps is good if you already have good normalmaps or a proper dynamic range or close enough quality height map.
And the effect if not abused can be quite fulfilling.