Hey i found a great product the other day walking through manhattan, a man was selling it in a booth. It's called the "MUNI Ticket Safe" and holds the little parking receipt against the window so the ticket is clearly visible and secure. I think you can get them online at http://www.muniticketsafe.com  I paid $6 bucks each in the street but they are cheaper online.

I use PARK-N-CLIP. It's a strong and clear clip that attached to the inside of my windshield. It holds the meter receipts perfectly plus I also use it to hold the receipt I get when I go to amusement parks and stadiums. It's about $5. Check them out at http://www.park-n-clip.com. The MUNI Ticket Safe is cool but I get more use from PARK-N-CLIP and its much easier to reach when its time to put the receipt in it. Plus, its Made in the USA.