Besides many governmental institutions, military forces and smaller national companies
I have trained IT-staff (or trainers or CCIE's or contractors) from the following internationally known corporations:

Aramco, Saudi	ABB	Arcor		Bayer AG
Bertelsmann	Bosch	BT	Cisco Systems	CMG, NL
Comtech (now Netbrain, DDLS)	Compuserve	Comparex	Commerzbank	Datakom Austria
Debis	DeTeSystem	Deutsche Telekom	Dimension Data	DeTeLine
Deutsche Bank	France Telekom	Equant	Friends Provident	Henkel
Horizon (now Azlan)	IBM	IZB	Manama University, Bahrain	MCI
MDR	Merck	MTS (now Azlan)	NCB, Saudi	NCR (several branches)
Netcologne	Neckarwerke Stuttgart	Petrolube, Saudi	o.tel.o	Porsche
Postbank	PDO, Oman	Qtel, Qatar	Shell	Siemens
SIMI	SITA (now Equant)	Slovakia Sporitelna	Sprint	Turkish Airforce
T-Data	Telemation (now DiData )	Telindus	Telstra	Thera Cosmetic
Marine Corps Warfighting Lab, Quantico, VA.	Thyssen-Krupp	Thyssen-Krupp	Thyssen-Krupp	VIAG Interkom
US-Airforce	US-Army	Convex, Portugal	Itergo, Hamburg	Best Buy, USA
Lucent, Poland	Santa Monica Networks	IBM, Austria	Comarch, Poland	DZSH, Germany
Swisscom	GAHS, Abu Dhabi	Amex Spie	Credit Suisse	Ericsson, Mexico
NextiraOne	Iteco, Nigeria	Al-Moammar,Saudi	Allianz-Dresdner	3KV
Great West	Nordstrom	US Postal Services	Getronics	Sensa, Iceland
Ethiopian Airlines	Telia Sonera	Polymedia Italy	Ernst&Young Poland	Pexim
Sunrise Switzerland	Fujistu	Praweda Indonesia	LogicaCMG	Econis
Telefonica Peru	Northrop Grumman	Alliant Technology	Recro-Net	EDS
Alcatel	Vodafone	HP