The first IBM-PCs used the Intel 8088, which was an 8086 with an 8-bit bus. The 8088 was continued to be used through the PC-XT line. The PC-AT was the first to use the next-generation 80286 series of processors. There weren't too many PCs that I know about that actually used an 80186 except for a few embedded systems. Amusing to think, how waaaay back in the early days, IBM originally considered 512K of main RAM would be sufficient (later revised to 640K). Of course this was back in the days when 48K or 64K maximum RAM was considered large.
I remember the first time I was learning 8086 assembly code, I was trying to remember why the segmented memory architecture looked vaguely familiar... Then I remembered the code I wrote on the IBM System 360 machines (at the university)... It was always amusing watching the reaction you get from folks when see they notice the "ASSUME NOTHING" directive.
The Z-80 series of CPUs were 8-bit was one of the early examples of CISC architecture microprocessors. From an instruction set perspective, it's an Intel 8080 on steroids. First experience in doing Z-80 code was on the old Tandy TRS-80 (model I no less). I do recall that there were quite a few micros based on the Z-80 back in the early 1980s -- just before IBM entered the microcomputer market. The only (recent) device I can think of that uses a Z-80 is the Nintendo GameBoy handheld game console (the more recent Advance uses a 32-bit CPU) -- and even that is pretty old.