Actually pretty much all versions of NetBSD run on CloudSigma as well as most BSD distributions. Not sure what the case is for EC2 but at CloudSigma you just FTP in a RAW ISO drive image. I found it pretty straightforward. I'm using FreeBSD primarily. See www.cloudsigma.com .
It has been my understanding that at least the fixed CPU instances on EC2 run on a custom Xen.