Although I certainly wouldn't claim this to be a complete list, the things that I would be looking at straight-off as regular maintenance would be as follows:
Rebuild the links database regularly if you use it on the front-end and publish content a lot.
Rebuild the search indexes if you use Lucene search if you are publishing content a lot.
Keep on top of the files generated in the data subdirectories.
I, personally, have never had to do anything with the databases themselves, but you may wish to keep an eye on any possible fragmentation if you're creating and deleting a high volume of content.
The above is all very obvious, and as you can see are only really applicable if you have a lot of publishing going on. By and large, Sitecore takes care of itself, and if it's serving from a database that's updated infrequently, then you should be fine. Just clean up the files when you don't need them and you shouldn't have a problem.
Some things you should perhaps consider (if you haven't already) with the set-up of the servers are:
Change the Sitecore logging level. By default I think this is set to Warn, and the logs can be quite chatty on occasion. If you're getting high volume, the logs may be unnecessarily large.
Install the Sitecore performance counters.
Change the Sitecore cache settings in the configuration. If nothing else, at least change the cache sizes to account for the memory available on each server.
If you're using 6.0 then upgrade to 6.1 at the very least. Sitecore 6.0 does not cache calls to IsUserInRole
, and so under load it generates a lot of unnecessary database traffic. I've seen this cause a lot of performance headaches.
It's all common sense, and probably not quite what you were hoping for but I've never had to do anything especially out of the ordinary. Then again, your idea of high-traffic could be quite different from mine.