There are some great ones here in this post at the Urban Muse, and nearly all apply to blogging as well as other kinds of writing.
Here are two of my favorites, quite germane to our project here:
Anyone can become a writer. The trick is staying a writer.
“I write when I’m inspired, and I see to it that I’m inspired to write at 9 o’clock every morning.” ~Peter De Vries
You can read all 30 quotes here.