Probably the best thing since sliced bread...Or just really useful :)
As a semi-frequent user of the Windows command prompt, I find it frustrating that it always opens in the same folder, in my case "C:\Users\Mark". I had previously discovered a power toy for Windows XP that enabled you to open a command prompt window in the current directory by right clicking on a folder in explorer, and clicking 'Open Command Window Here'.
Luckily, Microsoft decided that this was really sweet and actually integrated the functionality straight into Windows Vista/7, you just have to know how to get to it. To have it appear in the right click menu, all you have to do is press and hold shift and then right click on the folder you want to open the command prompt window at. You'll get it to appear in the right click menu, like the picture above :) Pretty Nifty!