I highly recommend Amazon AWS. You can continue to use WP Super Cache with Amazon S3 (for storage of your static files such as images etc).
For high traffic scenarios, you can set up auto scaling rules of EC2 server instances to set up new servers as needed (and cut them when not needed).
This is the best tute I’ve found on installing WP on EC2:
http://iampuneet.com/wordpress-amazon-ec2/