GRASS GIS on Mac OS X

Geo_DSDK version: 5.0.6.955
LizardTech (free registration required). Download the appropriate version for your Mac OS X version (Darwin 6.6 should be 10.2, and Darwin 7 - 10.3, no Tiger/10.4 yet).

Note: MrSID DSDK does NOT support GCC 4 on Tiger yet. If you need to use MrSID data in Tiger, get the DSDK for 10.3 and use the mrsiddecode program (that runs in Tiger) to convert to another format, such as GeoTIFF.

This is an easy one. It's really just a download, no installation needed. This is because the free, decoder-only libraries are static, and the lib/include folders layout is a bit non-standard.

$ cd path_to_folder_containing_geodsdk_source.tar.gz
$ tar -zxf Geo_DSDK-5.0.6.955.darwin.tar.gz
$ sudo cp Geo_DSDK-5.0.6.955/bin/* /usr/local/bin/

That last step is optional, but allows you to easily use the included mrsiddecode and mrsidinfo in the Terminal.

NOTE: if you are updating the Geo DSDK, since it is static you must rebuild GDAL for the update to take effect.