Let users rank pages I'd like to let users rank pages (thumbs up/down) and display “most popular” pages in ranked order. What's the best way to do this in Drupal?
Socially ranking content is a feature Drupal can provide very well. You will want to use a combination of modules consisting of something like: 


Views (used to build the lists of content and order them by votes / popularity),  
Voting API (a frame work for scoring / aggregation and will be used to record votes) 
Vote up/down (Vote up/down widget for user input on voting). you can even look at something like Fivestar. 


Once you have chosen and setup your voting widget on your content you will need to setup some views to display them in lists order by votes. Typically you will create a page view for any landing pages such as a Home Page and a block for displaying in sidebars on content pages. I also use Quicktabs for the Blocks so you can have a nice tabbed interface which lists content by Most recent / Highest Rated / Most viewed etc. 

On setting up the actual views you will need to add in fields for what you would like to show in each list. For example on a highest rated you might want the node title and the score for the node as voted for by users. Then you will add in a sort by option for the score so the list is presented in the correct order