I have not yet found a single backup solution which provides what I need for both database and file backup. So far I have used the following: VaultPress, ManageWP, BackupBuddy, SyncBackSE, and WordPress Database Backup.
Notes on what I have found below...
VaultPress: $15 per month per blog. Backs up continuously, but does not give you a single browseable backup archive that you can easily dig through with a folder directory listing. To me, this makes it cumbersome to retrieve a file from backup. For me, this solution is too expensive since I need to backup seven blogs.
ManageWP: Somewhere around $20 per month, but this also gives you a boatload of centralized mangement features and ability to backup/manage 10 blogs. Unfortunately I was not able to get this to work with Dropbox for my file backups (see notes on BackupBuddy below for possible reasons).
BackupBuddy: $100 per year (for 10 blogs). Works great in all sorts of ways, and worked great for me with Amazon S3, but due to a combination of limits in the Dropbox API and my shared hosting provider's PHP memory, it does not seem possible to get a backup working for more than 30MB of files.
SyncBackSE together with WordPress Database Backup plugin: This is my best solution overall, but it requires a desktop computer at home to be powered-on for nightly backups. SyncBackSE is a desktop app for Windows that costs about $30 one-time. This is set to backup any changed files each night via FTP. You have full control over what files are backed up and notification options. The files come down to my desktop and get further backed up as part of my Dropbox plan. No recurring costs other than Dropbox, which I had anyway. Then to handle the database backup I use WordPress Database Backup. Since I was not too happy with the requirement to have a powered-on computer I have been trying to replace this with BackupBuddy but as noted above various limitations are preventing a full switch to BackupBuddy.
If you can deal with some of the manual work involved in SyncBackSE, I think it is a pretty robust solution (when combined with a database backup plugin of your choice).