Recently I contacted a number of web font services and type foundries, to try and get a better idea of our clients options beyond Google Fonts. You might also find it useful:
|Service or Foundry||Email Support||Web Service||Self Hosted|
|Google Web Fonts (free)||yes||yes||yes|
|Hoefler & Co||no|
Note on Monotype
Monotype own FontShop, Fonts.com and Linotype (as well as Typecast). None of their web font licenses cover email. For that you have to go via Monotype Membership, which launched in Sep. 2014. The typefaces via that service are cleared for use everywhere, including email.
I found the book Responsive Typography by Jason Pamental really useful. Although web focused, he talks through the pros and cons of using a web font service vs. self-hosting, and outlines browser support for the different font formats such as WOFF and SVG.
Campaign Monitor also have an email specific write up, which is a good introduction to web fonts. Typewolf’s, ‘The Definitive Guide to Free Fonts’, lists the closest free alternative to every font on Typewolf. I’ve used this to find email safe alternatives to Hoefler & Co typefaces (Update as of November 4th, 2015 you can use H&Co fonts in email).