Safari 3.1 (and Webkit Nightly builds), Firefox 3.1, and Opera 10 support @font-face embedding for .ttf (TrueType fonts) and .otf (OpenType fonts). Internet Explorer version 5+ supports @font-face embedding for .eot (a proprietary embedded open type format) only.
Microsoft makes a horrible little font conversion tool called WEFT (Windows only) that you can use to convert most font formats to .eot.
CSS3.info has a nice, brief tutorial on how to use the @font-face rule. The site is a great resource for playing with CSS3 tricks (or in this case CSS2 proposed tricks).
There is a more thorough article on this subject on A List Apart.
Make sure any fonts you embed in a web page state that it is okay to do so in their licenses, as the font will live on your web server in a public directory, free for anyone to download. This use isn't always explicitly covered in the license, but you can usually contact the designer directly to ask. They usually let you use a font as long as you include a link to their page. I don't know for sure if Franklin Gothic Medium is approved for this use, but I doubt that it is.
Here are some a resources for free fonts. If you do enough digging, you can usually find a similar face that will work for you: