Bruce Murray Space Image Library
Asteroids and comets visited by spacecraft as of December 2012, in color, excepting Vesta [DEPRECATED]
The "click to enlarge" version has a resolution of 100 meters per pixel. Here is a version at 20 meters per pixel.
Below is another version of the same montage, except that the albedo is linearly scaled, meaning that Borrelly (with an albedo of 0.03) really is ten dimes darker than Steins (albedo 0.34). (Also available at 20 m/pixel)
Color images were not actually available for all bodies. There have been color images of Lutetia, Ida, Dactyl, Itokawa, Steins, Toutatis, Gaspra, Eros, Mathilde, Tempel 1, and Hartley 2. The others, including Braille, Annefrank, Halley, Borrelly, and Wild 2, were given a brown color to match the others.
Albedoes used for the composite:
Itokawa: 0.53
Steins: 0.34
Braille: 0.34
Eros: 0.25
Ida: 0.23
Dactyl: 0.23
Gaspra: 0.22
Annefrank: 0.21
Lutetia: 0.19
Toutatis: 0.13
Mathilde: 0.0436
Halley: 0.04
Tempel 1: 0.04
Borrelly: 0.03
Wild 2: 0.03
Hartley 2: 0.028