Update: A spokesperson for Citrix has clarified that what Citrix is releasing is not actually an IaaS: "The company is launching a product that public and private clouds can build their IaaS services on (they won't competing with established IaaS providers)."
Today Citrix announced that it will launch a new infrastructure-as-a-service based on the OpenStack platform. The new service is called Project Olympus and will be available for as both a public cloud and as a platform for private clouds. The first offering, which will include a "cloud-optimized" version of Xen Server, should be ready later this year.
The selection of OpenStack is important as various initiatives vie to become the standard for cloud computing. OpenStack is the open source initiative started by Rackspace and NASA and now supported by over 60 companies, including AMD, Canonical, Cisco, Dell, Intel and Citrix. Other potential cloud standards include Red Hat's Deltacloud and the NRE Alliance's proposal.
Citrix will be taking on established IaaS providers like Amazon Web Services, Joyent and Rackspace. Dell and HP are expected to launch public and private IaaS solutions as well. It might be worth noting though that both Dell and Rackspace gave positive supporting quotes in the announcement.
Also, a few IaaS providers have been acquired by telcos this year, meaning that much of the competition has very deep pockets.