Web Font Formats:
EOT, TTF, OTF, CFF, AFM, LWFN, FFIL, FON, PFM, PFB, WOFF, SVG, STD, PRO, XSF, and the list goes on.
Services can allow for fonts you wouldn't otherwise have access to, allow you to use the font legally, and deal with the delivery for you (e.g. serve the fonts through a CDN for you). Here's some:
Cloud Typography, Typekit (Annual), Fontdeck (Annual), Webtype (Annual), Fontspring (One-time), Typotheque (One-time), WebINK (Monthly), Fonts.com (30 days), Fontslive (Annual), Google Fonts (Free), Kernest (One-time), Font Squirrel