Commodore 64

Axel's C64 Emulator
New C64 emulator project for Windows. Includes the source code as a Visual Studio .NET project.
http://www.ac64e.com/

CCS64
Commodore 64 emulator for MS-DOS, Windows and Linux/Unix. Shareware.
http://www.computerbrains.com/ccs64/

C64S
European C64 emulator for the PC. Includes links to web sites and software.
http://www.phs-edv.de/c64s/

ec64
An open source emulator for Linux. Also features Commodore hardware information.
http://unusedino.de/ec64/

FC64 - Flash Commodore 64 Emulator
Low level Commodore 64 emulator for Flash Player 9, written in AS3, released under the GPL.
http://codeazur.com.br/stuff/fc64_final/

Frodo
An open source emulator specializing in raster effects for AmigaOS, BeOS, MacOS, RiscOS, Unix, and Windows.
http://frodo.cebix.net/

gp32 Frodo
Frodo ported to the GP32.
http://gp2x.org/gp32/frodo/

Hoxs64
A new freeware Commodore 64 emulator under development for Windows.
http://www.hoxs64.net/

JaC64
Presents this open source Commodore 64 emulator which can work as stand alone application or a Java applet within a web browser. Includes documentation and an online demonstration.
http://www.jac64.com/

OpenC64
An open source emulator for Windows using the .NET Framework.
http://sourceforge.net/projects/openc64/

Personal C64
C64 emulator for MS-DOS and Windows. Development stopped in 1997 but the source code and executables are available for free.
http://www.zimmers.net/anonftp/pub/cbm/crossplatform/emulators/msdos/pc64/PC64-en.html

Power64
Commodore 64 emulator for the Mac OS. Shareware, fully functional for 10 minutes until registered.
http://www.infinite-loop.at/Power64/index.html

VB64
A freeware emulator for Windows written in Visual Basic.
http://vb64.emuunlim.com/