Implementing Generic Caching

I develop for a large, high-availability website, with hundreds of thousands of daily users. As such, we need to cache a lot of data in our web-server memory (which is cheap) to save numerous hits to our main database cluster (which is very expensive). I would imagine the desire to improve performance by saving on database hits is common across many web applications – and caching frequently used data is often seen as one of the best ways to solve this problem.