proteus 8086
To date I don't recall seeing any SPICE simulator which can simulate the 8086. Proteus is quite a nice software, considering its size and ability to simulate some of the common microcontrollers and PICs.
It's ashame the simulation model library is quite limited, and modelling a medium complex IC can be quite a trying experience for new comers.
Still, I've used it in my work quite a bit to verify some test specifications in order to troubleshoot some of the PCBs I'm repairing. Pretty accurate, I should say.