Recommended Free Fonts
Devanagari:
Siddhanta (Excellent support for Vedic texts)
Martel (Google)
Vesper (Google)
Sahitya (Google)
Sanskrit Text (Microsoft)
Kokila (Microsoft)
Arial Unicode MS (Microsoft)
Lots of fonts at http://www.devanagarifonts.net/ (http://www.devanagarifonts.net/fonts/toprated.html)
Grantha:
Kannada:
Goda and GodaGr Supports Taittiriya and Samaveda Svara-s
Vagisha and VagishaGr Supports Taittiriya and Samaveda Svara-s
Tamil:
Lots of fonts at http://azhagi.com/freefonts.html
Telugu:
Pothana2000Vedic Supports Taittiriya Vedic Svaras
Couple of good looking fonts at http://www.teluguvijayam.org/gumi.html
Also fonts for all scripts available from http://www.ildc.in/
Roman IAST/ISO15919: