One of my favorite plugins for looking at WordPress memory usage has always been TPC! Memory Usage [don't download this version]. Unfortunately, it was last updated for WordPress 2.9.2 and a few things have changed since then. As a result, the plugin was producing a number of errors.
Not one to be put of by a bit of dirty work, I went ahead and updated the plugin for WordPress 3.8. Screenshots are attached.
Since I know a lot of you run into memory/performance issues with discount-grade hosting, I thought this might be a useful thing to share.