Obviously that falls into it "it depends on what you're looking for" territory, but some of my favorite (AFAIK) open source fonts: - Arimo, Tinos, and Cousine:

Obviously that falls into it "it depends on what you're looking for" territory, but some of my favorite (AFAIK) open source fonts: - Arimo, Tinos, and Cousine: The "Croscore" fonts designed by Monotype's Steve Matteson as metrically-compatible replacements for Helvetica, Times New Roman, and Courier, respectively. (Red Hat's Liberation fonts are basically the same.) - Adobe's Source Code, Source Sans, and Source Serif Pro fonts: now that Source Serif has its italics (and Google Fonts looks like they've finally bothered to update), these are pretty terrific. - Charter: an old font that's actually really high quality. - The Computer Modern fonts from TeX: easy to overlook if you're not using TeX, and makes anything you use them with look like you are using TeX, but they're good typefaces. - Cooper Hewitt: a sans serif designed for the museum of the same name. Maybe the most relevant in a discussion about Neue Haas Grotesk, since it's another font with a strong sense of design and purpose, and, well, isn't Helvetica. :) Most of the Google Fonts can be downloaded and self-hosted, FWIW, and you can use Font Squirrel to subset them and make them extremely small and fast. I do that with a few commercial typefaces on my own web site. (Commercial typefaces that actually allow this with their license!)