Hi Ed,
Do you know how they got hacked? The best solution would be to patch the holes that already have rats coming through them, then work towards other holes they haven't discovered yet.
The trouble with getting your site compromised it that even after you get things back up again, you don't know if the "backdoor" they may have used is still there.
I would recommend a recent version of backup buddy (you can pull it from one of the PLR blogs from this month or PM me for a copy) for the backups but also because it now includes a malware scanner. In fact, Scott includes a couple security related plugins on those blogs. I can pull the list of plugins for you or you can install one and check it out.
There are a number of products out there talking about how to secure your site and I believe there is one specifically about securing WP sites in the Gold members area.
Generally, make sure your passwords are secure, that you trust the plugins and themes you're installing, stay up to date on WP minor revisions (security updates like 3.2 to 3.2.1, versus the major feature upgrades of 2.9.2 to 3.0).
If you always use the same computer to access your sites, you can lock thing to the IP address assigned to your computer. The downside is that if your ISP changes your IP you'll have to go in and do some things manually before you can access WP. I believe WPLockdown in the Gold archive covers that nicely, but I'm not sure if the plugin portion is out of date.
HTH