Docker runs on linode and digital ocean (https://github.com/dotcloud/docker/issues/469, https://github.com/dotcloud/docker/issues/424) by loading a custom kernel. Assuming the requirements for Flynn aren't much more than Docker, the whole stack should run there as well. Easy for end-users is probably a matter of opinion, especially until Flynn releases some code.
Digital Ocean: http://kencochrane.net/blog/2013/06/running-docker-on-digita...
Rackspace: http://kencochrane.net/blog/2013/05/running-docker-on-racksp...
Linode: http://stinemat.es (site seems to be down at the moment)