Google App Engine is a unique cloud platform and you won't find any other similar hosting. Except maybe hosting your own AppScale platform somewhere : http://code.google.com/p/appscale/
But I don't think it's ready yet.
The closest to GAE would likely be some sort of Heroku-clone for Python. I know of two upcoming services :
- http://www.djangy.com
- http://stable.io
You could also try Media Temple Grid Service which has Django grid containers : http://mediatemple.net/webhosting/gs/features/containers.php#django
