I have seen increased 'HEAD' requests in my webserver access.log. What are these requests for? Should I disable this method in my webserver configs?
No.
Relevant quote from the link:

HEAD
Asks for the response identical to the one that would correspond to a GET request, but without the response body. This is useful for retrieving meta-information written in response headers, without having to transport the entire content.

If you disabled it, you'd just increase your throughput cost. A person can get the same information with a GET, so if they were trying to do something malicious, they could just use a GET. Except, this way, they're being nice and not forcing you to send the request body.
EDIT: I don't know what the requests would be from, although I can certainly think of uses. Anyone else who knows or wants to chip in, please do so. I'm kinda curious, myself. Hence, community wiki.
