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.
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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.