Printing Online

Printing postcards, posters, buttons, bags, t-shirts, cups, etc, etc

     Just my reference on what I've gone with over the years.  Not necessarily the cheapest or the best quality but what best suites what I needed (maybe cheapest for that particular item or whatnot).

Postcards
GotPrint.net - Consistently low price for cards and postcards, their regular price often equal to or cheaper than the promotional prices of other sites.  Quality remains very good though.

Bags
Zazzle.com - Good for few quality bags and lets you add an image with any number of colors.
QualityLogoProducts.com - Cheap and generally can find under $1 at low quantities.
TotallyToteBags.com - Quantities in the range of 100s, but under $1/bag and free rush, good selection etc.
4imprint - Relatively quick turnaround (3-days) and many items but no items under $1 unless you order several hundred in quantity.
CustomGroceryBags.com - Cheapest price and best looking quality.  However, the turnaround seems longer and requires higher minimum quantities.

Buttons
PureButtons.com - Very low price buttons and small minum quantity of 50.  Wide selection of shapes and sizes.