If you work with lots of Fonts, sometimes you might want to preview them before installing.

Do this by double clicking on them in the finder or dragging them to the Font Book icon (in the Applications folder). Font book will open a new window for each one, with a large sample of the font. However these windows will cascade and overlap, so you can only see one at a time.

Using exposé (F10), you can spread out all the windows and preview all the fonts side by side. To install a font, click on its window to bring it to the front, then click install.