When I had my little desk set up at my old apartment before Gina and I got married, I had a couple of things tacked to the bulletin board hung on the wall above where I would write. One of them was a collection of pictures from magazines that I'd pulled to use for setting or character inspiration. The other thing were some quotes that I found inspiring. They were reminders to me to just keep writing no matter what.
Looks like I am not the only one. Tobias Buckell does it too and he shares those quotes on his blog. I'd share mine but I can't remember any of them. When I get the bulletin board and all of its contents out of storage I'll share them.
And read the responses to Tobias' post. There are many more good quotes there.