Exchange Hosting by Hosting.com [formerly known as Invotion]
http://www.hosting.com/hosting/exchange/exchange-hosting-benefits.asp

Webville Exchange Hosting Service
http://www.exchangehostingservice.com/

NasStar Hosted Exchange
http://www.hostedexchange.com/

The Message Center Exchange Hosting
http://www.themessagecenter.com/services_exchange_plans.html

DeSaMa Technology – Exchange Email Hosting Solution
http://www.desama.com/

1&1 Outlook Exchange
http://www.1and1.com

BRI Hosted Microsoft Exchange 2003
http://www.brnets.com/Solution-Center/Microsoft-Exchange.asp

Hostbasket Office Mail Hosting
http://www.hostbasket.com/e-mailhosting/officemail.shtml

Hosted Microsoft Exchange 2003 by JustExchange
http://www.justexchange.com/exchange_hosting.htm

Exchange Hosting Solutions by HostLabs
http://www.exchangehostingsolution.com/