Preview from 10.3 should work under 10.6 - there's no obvious reason to tie it to a specific OS version.
I keep Grab 1.0 around from 10.0 because it will work if DVD player is running, unlike the later Grabs. Along with Picture Viewer.app from OSX Beta, because (unlike Preview) it reads image files based on internal format. In other words, it will open an image even if it has an incorrect extension.