There are a lot of spectrum emulators out there. You’re not just limited to emulation on a PC either, there are excellent emulators available for almost every PC, console and hand held you can think of. I have used them on Amiga, Xbox, PSP & iPhone.
The emulator that I find best to use on a PC is called “eightyone” and is by Michael D Wynne.
Some of the best features are the fact that you can choose to laod games the old fashioned “slow” way via the emulated tape loader option or have them load pretty much instantly with the “Flash Load” option.
There are also some very good TV tools that allow you to simulate that flickering / ghosting that all good spectrums had when viewed on a TV!
Download it here: eightyone.1.0.a