This example shows how to use the free Linux Libertine fonts on writeLaTeX. The Libertine font family provides serif fonts similar to Times New Roman.
The source code is based on The LaTeX Font Catalogue.
The XITS fonts provide a Times-like serif typeface for mathematical and scientific publishing. They provide a version of the STIX fonts enriched with the OpenType MATH extension, making them suitable for high quality mathematical typesetting with XeTeX and LuaTeX. XITS fonts are free and open source.