Is there a list somewhere of all known x86 CPU identifiers (such as „x86 Family 6 Model 15 Stepping 13”)?
Because it is a CPU command, the obvious place to find a list is in the technical documents (programming specifications) of CPU vendors. There’s a gotcha however because after the Pentium, AMD split off and started creating their own CPU architecture which over time became less and less compatible with Intel’s (ie different sockets, different features, even different instruction sets to some degree). As such, you will also need to check AMD’s tech-docs, lest you have incomplete information (after all, Intel has no motivation to include a competitor’s models in their documentation—in fact, the term ‘AMD’ does not even occur in it).
Another thing to note is that there are other CPU vendors in addition to just Intel and AMD (believe it or not, this is a big surprise to a lot of people). There are obsolete vendors like Cyrix, some who no longer produce CPUs, and several others who produce CPUs for enterprise servers (IBM) or embedded devices (ARM) and such instead of consumer equipment. If you want these as well, then you will need to research them individually because there is no central location to look (Wikipedia has some information, but it is—not surprisingly—woefully incomplete), while CPU World has a lot more (go figure), though again, it is likely to be incomplete, especially since new CPUs are produced regularly.
Note also that many vendors do not include the
Ask and you shall receive: http://www.cpu-world.com/cgi-bin/CPUID.pl
While this page is not necessarily complete it does seem to have quite a large number of CPUIDs... here's a reasonably up to date example, the i3 370 Mobile Processor: