Vic 20

PCVIC
Upgrade your PC to a VIC-20. Runs on MS-DOS, OS/2 or Windows.
http://wwwhome.cs.utwente.nl/~schooten/software/pcvic.html

Pfau Zeh
VIC-20 emulator for Win32 and Linux.
http://pfauzeh.classicgaming.gamespy.com/pz_main.html

Power20
VIC-20 emulator for the Mac OS. Shareware, fully functional for 10 minutes until registered.
http://www.infinite-loop.at/Power20/index.html