Is there a way to find most voted questions from a certain time period, e.g from the last month? Now I can find a tag and then select "Votes" but AFAICS this is list of "all time most voted".
If you know sql, or are willing to learn, check out http://data.stackexchange.com/ - it contains a relatively recent copy of the site, with some things (like voting records) removed.
You can use a little SQL to find something similar to what you need - such as highest voted posts that were originally created during a specific time period.
I imagine these search operators didn't exist when this question was posted but it is possible to restrict the search to posts last active or created within a specific date range.
So searching for
is:question created:2013-10-21..2013-11-20 and selecting the "Votes" tab will bring back the top voted questions in the last month (at the time of writing).