I've consulted to a lot of big and small clients over the years, mostly in my work within a computing company.
The list is not exhaustive and I've only listed those that I remember.

While at Computer Technology Express we sold over 1100 copies of SendMail (a UNIX and NT Mail Server software product) to companies all over Australia. Every one of those sites required my personal attention when the customers wanted support, which was often; I don't remember them all but I do remember some of the asinine things highly paid IT installers were hung up on when doing a simple installation with adequate instructions.

Here's an abridged list of some past clients along with what I needed to do for them (it goes without saying that due to the sensitive nature of much of the work I do, I've signed "non disclosure" agreements willingly. I won't tell you their business and I won't tell them yours.

• Nine MSN - Designed the first DNS for their NT 4.0 servers for their consultants before they went live.
• Optus - Designed the setup for their first NT based mail server
• Telstra - Designed the setup for their first NT based SendMail server
• United Airlines - I was asked to show them an easy, rock solid and reliable way to readily move development SQL files to a live public SQL server.
• Lucent - Consulted to them and solved a faulty enterprise wide CRM installation by their incompetent vendor, when multiple use of records caused a database corruption.
• Melbourne Childrens Hospital - Consulted on the first Australian installation of a "super scoped" multi block site wide IP Address management system.
• Rand Merchant Bank - Consulted on the first Australian installation of a networked 256 online disk CD-ROM tower server.
• West Australian Newspapers - Designed a complicated NT 4.0 based DNS with failover system.
• The Trading Post - Designed an enterprise wide digital imaging storage and transfer system.
• Australian Parliament House - Consulted on the implementation of a site wide IP management system.
• Adcorp Australia Ltd - Consulted and reported on the design and security vulnerabilities as well as optimization of the SQL databases for their Recruit Manager software, which is the back end of News Limited's www.careerone.com.au, then the largest recruitment site in Australia.
• Computer Associates - Installed, rolled out, commissioned and then managed the first successful Australian installation of their Accpac Enterprise Accounting for MS SQL. The North American system had to be largely modified for localization on the back end SQL.
• GoldMine Software Australia - Consulted and solved multi user database corruption problems caused by issues involved with Opportunistic File Locking on NT Servers as well as multi user performance issues with Goldmine access to systems re-hosted to MS SQL.
• Telstra - Designed a secure and encrypted field dial up access solution for Telstra technicians to log into Telstra's Netware network.
• Australian Flora - Modelled, wrote, installed and rolled out a new SQL database from the ground up that could reliably sort plants via their taxonomic keys. The objective was to ensure that all "primary and foreign keys" were integer based and to eschew as much as possible "text searches" to ensure maximum speed. The previous databases used around the world had been designed by botanists or designed by people instructed by botanists. My lifetime interest in and knowledge of botany ensured success.