Spectaculator for Windows
This emulator is featured in the Easy Start Guide. It is an excellent choice if you have Windows XP, since it installs automatically, is very easy to use, has loads of options and emulates practically every feature of the various Spectrum models.
The emulator is distributed as a 30 day trial, after which you will need to purchase the program from the official website.
You can either download the emulator directly, or consult the easy start guide for an explanation of exactly how to download and install this program.
The screen image here shows the program running on Windows XP and emulating a Grey Case +2 model Spectrum.