Where do you store steam keys?

TXT or Evernote.

I use Notepad ++. Simple, quick open.

google docs, do you want the link?

Where the sun don't shine! ;-p

Evernote

Quanti italiani :P
Comunque io uso notepad++ se le key non sono troppe, altrimenti excel, colorando di rosso le caselle delle key usate

I use an Excel file with multiple columns. More details here.

Well thanks Yirg for bump I didn't see that topic before..
& thanks xXToXiiCDOGZz for the topic itself because it start to make me wonder is my method is safe enough & I just decided to move my all keys to secure txt file (secure aes512 method) just in case someone hack my comp & find my all keys in one simple txt file ^^