What are and which is highest IM or NM or FM or CM?

IM is the highest

aside from GM

Is a 2500 GM stronger than a 2600 FM ? 

hard to say, maybe the FM is just really great at that time control?

Kramnik was a 2600 FM and jumped straight to GM from that , he skipped IM !  I played a 2500+ FM once and he is now a GM .

Perhaps a more interesting question is who is the highest rated IM/NM/FM. Who has a very strong rating but is missing the norms?

IM is the second highest title, then FM, NM, last is CM.

The 2600 FM would certainly have the norms then...

Out of the list of all the masters mentioned in the list IM is the highest. 

Of course GM is the highest title, but out of the one's mentioned in this topic IM is the highest. 

Kramnik was a 2600 FM so appaerently he didnt have the norms for either IM or GM yet , but Kasparov got him into the Olympiad where he had such a tremendous performance that he gained the GM title , he skipped IM as have a few others .

GM>IM>NM>CM>FM

FM>CM

GM>IM>FM>CM>NM

I actually met this guy in person. He is a friend of my chess coach from millitary. He quit chess because he wanted to pursue his career as an elctrical engineer. He is a Fide Master and has a peak of 2481.

CM and NM are roughly equal . CM is based on fide rating where NM is normally based on national ratings ( like USCF )

So. It goes CM > NM > FM > IM > GM

There are equivalent titles for women. The only difference in requirement is 100 rating points less than the standard title's requirements.

A CM is a Candidate Master.

A NM is a National Master.

A FM is a FIDE Master.

An IM is an International Master.

A GM is a Grandmaster.