From the top of my head, here are the know planets destroyed for war purpose in the Star Wars Galaxy :
Mandalor
Taris (admitedly, the less badly damaged of this list)
Geonosis (dat time jump!)
Alderaan ( duh... )
Cardota, Courtsilius, Hosnian, Hosnian Prime and Raysho (had to look those one up, they're not even named in the movie... sic)
Ilum ( It's not yet canon that the Starkiller base was Ilum I think, but come on... )
The two first were destroyed millennia before the battle of Yavin. Geonosis about 20 BY (before yavin), the six last were destroyed ~20 After Yavin in maybe a single day.
Things are looking grim for this galaxy...