Bloody hell, Kerli! She and Elina must be the clear frontrunners on name alone.
Other people we know:
Koit Toome (1998) and Laura (from last year as well with Suntribe in 2005) with a song written by the legendary Sven Lohmus (who else?)
Ivo Linna (1996)
Lenna (2005 with Vanilla Ninja as well as runner up in EL 2012, also took part in EL 2014)
Daniel Levi (runner up to Stig and Elina)
Janno Reim (lead singer of Super Hot Cosmos Blues Band and thus runner up to Tanja)
Liis Lemsalu (frequent participant <3)
Rasmus Randvee (participated with Facelift Deer in 2013 and his song this year is cowritten by Ewert from Ewert and the Two Dragons)
Seems a more pop focused lineup than previous years so far, still pretty shocked Kerli's taking part!
A five minute version of Ivo's song is up; it's rubbish:
https://www.youtube.com/watch?v=uC8yhiCVxB8