This is the biggest map I've been able to make of Second Life (abusing the Mappa Novus tile server, sorry about that) without hitting the image size limit in ScreenGrab. Click through the thumbnail for the 13MB version, or try this dynamic map.
There's also an official version of the map API [documentation], but this version seems to show a smaller section of the world (update: the smallest regions only show up at the highest zoom level, so aren't visible on this image):
SignpostMarv Martin has made some images of Agni, the primary Second Life grid:
A monochrome "distribution" image:
and a large whole grid image: