Backing up a 400-500 GB database on MySQL/Amazon RDS?
RDS provides automated backups as a feature.  Those backups are system automated (persisting through the life of the RDS instance), or user initiated (persisting outside the life of the RDS instance).  They also automate binlog backup for point-in-time restores.  But you can't take those backups out of the RDS service, as it's all hooked together for automating restores, etc.

FAQ: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/RDSFAQ.Backup.html

I assume you want a backup outside of RDS.  mysqldump would be the only way to do it, and unless you use some creative ETL to facilitate some sort of daily delta, you might save time.  Otherwise, that's a good chunk of data to backup on a regular basis.