First Appearance Ahsoka Tano

The Clone Wars animated series ran from 2008 - 2012 returning for 13 episodes in 2014 and again for a final 12 episodes this year.  The series did an excellent job of fleshing out the story of Obi-Wan Kenobi and Anakin Skywalker's involvement in that fabled conflict.  It also introduced many memorable characters with none being as important as Ahsoka Tano, Anakin's Jedi Padawan.  She first appeared in the theatrical movie The Clone Wars on August 15, 2008.  This was followed by her appearance in two Star Wars comics from Dark Horse: The Clone Wars #1 and The Clone Wars - Shipyards of Doom both released in September.  The animated series began on the cartoon network on October 3rd.

The Clone Wars #1 edges out Shipyards of Doom by a few weeks to be the first appearance of Ahsoka Tano in comics.

Star Wars: The Clone Wars #1a - Dark Horse Comics, U.S. (September 2008)
Direct
1st appearance of Ahsoka Tano in comics

Star Wars: The Clone Wars #1b - Dark Horse Comics, U.S. (September 2008)
Newsstand
1st appearance of Ahsoka Tano in comics

Ten lucky retailers received 100 copies each of the Dark Horse 100 variant of The Clone Wars #1.

Star Wars: The Clone Wars #1c - Dark Horse Comics, U.S. (September 2008)
Dark Horse 100 variant
1st appearance of Ahsoka Tano in comics

The digest-sized The Clone Wars series also began in September 2008.  This format proved successful with younger readers and this title ran for 11 issues ending in 2013.

Star Wars: The Clone Wars - Shipyards of Doom a - Dark Horse Comics, U.S. (September 2008)
digest-sized
2nd appearance of Ahsoka Tano in comics

A Target store exclusive issue of Shipyard of Doom was included with DVD and Blu-ray copies of The Clone Wars movie released in November 2008.

Star Wars: The Clone Wars - Shipyards of Doom b - Dark Horse Comics, U.S. (November 2008)
digest-sized
Target exclusive
2nd appearance of Ahsoka Tano in comics

When the Clone Wars animated series ended, Ahsoka had walked away from the Jedi order.  She next appears in the final episode of season one of the Rebels animated series.  She is due to make an appearance in The Mandalorian season 2.