From the perspective of a GIS professional, I would add the PostGIS extension for PostgreSQL. The depth of spatial analysis options in PostGIS combined with the reliability and performance of PostgreSQL make a great combination. Throw in the cost savings compared to running MS SQL Server/Oracle + ESRI ArcGIS Server and I'm not sure why more GIS shops don't make the switch (Fear of FOSS, the command line, or having to assemble your own solution?).
I'm not sure why more GIS shops don't make the switch
As another GIS professional I've found that the answer to this question in roughly 100% of the cases is that they have some important application (either third party or in house) that doesn't trivially talk with PostGIS and they don't see the cost saving once they've factored in all the migration costs. So vendor lock-in basically.
