Google has an amazing collection of fonts in its free to use web directory. They can be downloaded to your computer or used in a web design project. The purpose of it is to give people a lot more choice than the standard set of fonts you get with your machine.
If you're a huge Google fonts user like myself you'll find this tool very useful.
Skyfontsis a small program that allows you to download and sync fonts to your computer. They have partnered with Google to offer the fonts to anyone and everyone for free. They're ideal for print use but can of course be used when mocking up websites in Photoshop. If a font is updated, that update is automatically synced.
Once you've installed the program you'll want to add fonts. To add fonts to your collection you have to go to the Skyfonts site, hit the "Browse Google Fonts" button and you'll be given a very good font preview box. The fonts are shown beautifully, unlike Google's own site.
You can then quickly browse through the fonts and add the ones which pick your fancy.
The service is completely free to use and I highly recommend it to anyone who's into their typography.