Many people have commented that strong commercial support is what enterprises need before they can invest in open source technology. Strong support is available worldwide from a number of companies.
The authors work for 2ndQuadrant, which provides commercial support for open source PostgreSQL, offering 24/7 support in English and Spanish with bug-fix resolution times.
Many other companies provide strong and knowledgeable support to specific geographic regions, vertical markets, and specialized technology stacks.
PostgreSQL is also available as a hosted or cloud solution from a variety of companies, since it runs very well in cloud environments.
A full list of companies is kept up to date at http://www.postgresql.org/support/professional_support/.