Dirkey is a Windows Explorer tweak that allows you to access your most frequently used folders in any Open/Save dialog with keyboard shortcuts.
The program works on any standard Window application. This means that anytime you're on a Open/Save dialog, you can press the correspondent key combination to instantly open the folder where you want to open or save that file. These folders are saved in Dirkey's settings as bookmarks and can be managed from the program's configuration options. Another way to bookmark folders is simply by opening them and pressing Ctrl+Alt plus the number you want to assign to it.
The downside to Dirkey is that it's a bit complicated to set up, plus the fact that you can't customize the keyboard shortcuts (you'll have to stick to the program's defaults, Ctrl plus a number).
Open your favorite folders from any Windows Open/Save dialog in a snap.