Many times I find myself having to mock-up designs on various items such as bags, DVD covers, coffee mugs, and other various gift items for clients. Having an archive full of blank photos of such items goes a long way in making the task easier. 
Diegomattei has a collection of over 250 blank design template items you can easily drop your artwork onto in Photoshop for quick mock-ups to show off to your client, or use in an ad. The site is in French, but the 67MB MediaFire download link is at the end of the article, called Creative Collection.
