Here is a list of extensions, that i use but have found not to be in core yet, some of them not even EXT or ARB. Those are GL 2.1 extensions, some of them have been included in GL3, but not all. I am not sure, whether the ARB plans to release a GL 2.2 for all those "lazy CAD developers" i am more concerned with GL3 development. Still it is a bit crazy that there are extensions, which are used by nearly every GL application for many years, but have not yet been promoted to core, ARB or even EXT.
Not in GL3, not in core, most not even ARB:
Included in GL3, but not ARB or in core in GL 2.x
Please correct me, if i got something wrong here.
Especially texture compression, anisotropic filtering and v-sync should become core soon, IMO.
There are certainly more extensions to be put on that list, but those are the ones, that i found in my code to be referenced.