Ubuntu Trusty Tahr is going to be released on April 17th 2014. Meera Tamil font, a free licensed unicode font for Tamil will be available in this release. The font is already available in Debian. In both Ubuntu and Debian you can install the font by sudo apt-get install fonts-meera-taml Thanks Vasudev for packaging it for Debian.
A few months back, we started fixing the collation rules of Indian languages in GNU C library. Pravin Satpute prepared patches for many languages and I prepared patches for Malayalam and Tamil. Later Pravin enhanced the Tamil patch. You can read the rules used for Malayalam collation here[PDF document]. Tamil patch was applied to upstream, but the bug is still open since there is some confusion on the results. Before reading the below discussion, please read the discussion happened in the bug report : [ta_IN] Tamil collation rules are not working in other locales ...