Please visit this and associated pages to see three Devanagari Unicode font
sets viz. Chandas, Uttara and Siddhanta. These fonts have also variation
versions incorporating extra characters and ligatures used specifically in
vedic sanskrit. (Some of them are yet to get a Unicode value).
http://svayambhava.blogspot.com/p/siddhanta-devanagariunicode-open-type.html
These are free for use and adaptation as per the information on the
relevant web pages.
It is suggested that you use any of the suitable fonts from this set as the
default devanagari font for your browser. These fonts may also be added to
our Input methods by the 'narayam' team. Administrators may please consider
along this direction.
-ViswaPrabha