There is nothing more likely to instill a creative block than a blank white screen in Illustrator or Photoshop. For some reason if you are feeling slightly less than inspired that empty space can appear huge and overwhelming especially on a 27" screen.
The solution that works for me is to get scribbling!
On a scrap of paper, on the back of an envelope, on your tablet with a stylus, it doesn't matter. For some reason that familiar, friendly feeling of a pencil in your hand, helps to get the synapses pinging and the link between hand, eye and brain whizzing along.
The image above (done in biro on a scrap of paper) was the original sketch for an Illustration that I supplied to iStockphoto.com, it was scanned and used as a template layer in illustrator.
I have also roughed out ideas on my ipad using a stylus and the penultimate app. These don't need to be finished illustrations, not even close, but what they can be is scraps and jolts of ideas, little reminders that tag inspiration before it disappears. They can then be returned to and mined when your idea store is running low.