The important thing to realize about clouds is there will not just be a few of them. This is a new computing paradigm. There will be public clouds, private clouds, research clouds, clouds for hire and even "black clouds" used by security experts.
To me this looks like a job for open source.
It's important to note that things like Google's new Cloud Foundry are not just building tools for use on the Google AppEngine cloud. These are designed as general purpose tools for use on all clouds.
Cloud security tools can be tested in the cloud, can be quickly distributed among clouds, and (since cloud owners are enterprises, not clients) be supported by a business model that works.
So if you want to make money in 2009 I offer this bit of advice.
Build yourself a police station in the clouds, using open source, and develop services clouds will need to protect themselves.
Cloud owners will be glad you did.