Firefox (Windows/Mac/Linux): Google provides an astounding number of services. GButts is a small Firefox plugin that creates a "speed dial" toolbar to help you quickly jump to your favourite service.
If you only use one or two Google services, say Gmail and Google Reader, you may not need quite need the speed Gbutts provides. If you partake of more than a few of the 48 services currently offered however, Gbutts is a handy tool for zipping about.
You can select which services you want to appear in the list and how they will be displayed. The menu is available either as a toolbar or a drop down menu. We're using the drop down menu above, nestled between the address bar and the quick search box. You can also specify if the shortcut will open in a new tab and whether or not that tab should be in the foreground or background.
If you'd like to take a screenshot tour before installing, make sure to check out the screenshot-laden write up at The How-To Geek. GButts is free and works wherever Firefox does.