I just found this and thought I might share. Google has a giant pile of fonts, free to use in your web app.
Google is nice because that provide you not only with the font, but a very high availability server to grab the font from (rather than host it on you server) The also provide you with the syntax on exactly how to download it (Example): http://www.google.com/fonts#UsePlace:use/Collection:Source+Sans+Pro
If you simply set app to the App.HTMLheader to (In this case) <link href='http://fonts.googleapis.com/css?family=Source+Sans+Pro' rel='stylesheet' type='text/css'> Goggle allows you to select all the members of the font family and generated the link for you. (I suck at CSS so for me its wonderful)
They you can download the font to your Mac and it designs and works seamlessly with Xojo Web.
Makes me wonder; What other stuff is out there that I'm missing?