Tamil 99 is a fast and simple typing keyboard layout approved by the Tamil Nadu Government. The layout, along with several monolingual and bilingual fonts for use with the Tamil language, was approved in year 1999.
Adding Tamil 99 Keyboard in Windows (including other Tamil Keyboard layouts)
Adding Tamil 99 Keyboard in Ubuntu 14.04 (including other Tamil Keyboard layouts)
See http://tamil99.org/ for more details relating to Tamil99.
Other relevant links
Tamil99 keyboard stickers
(Can get it printed in sticker print shops)
Tamil typing methods (different keyboard layouts for Tamil)