From free business cards to discounted postcard printing, I like both these services, which make it easy to upload or create your own designs for postcards, business cards and all manner of printed goods (mugs, wedding invitations, sticky-notes!).  Vistaprint may be best knows for their free business card offer — it's real, along with other amazing free and deep discount loss-leader offers.  They use these offers to engage then upsell you 2-sided color printing, better paper, faster shipping and other items "Why yes, my design does look good on a mug and a refrigerator magnet…. I think I'll order a couple."  They're the best source for free business cards, but their regular discounted printing services are still a good value – especially for 2-sided, 4-color printing.  If you end up with more than free business cards in your cart, try some of the other links for a better final price (I use the 80% OFF Business Cards for the best value on premium business cards.)

Uprinting sales process is a little more straight-forward, with faster standard turnaround times. Both offer excellent prices and customer service.  Use the links below for some of their best offers:

Vistaprint:
Use this link for 250 Free Business Cards.
Use this link for 80% Off Premium Business Cards & Free Return Address Labels.
Use this link for Free Shipping and 25% OFF Sitewide on orders of $50 or more.
Use this link for 500 Business Cards for $1.99 (Limited time offer).
Use this link for 1 Photo Mug for $1.99. (yes, your mug on a mug makes a great gift!)
Use this link for 30 Free Wedding Save-the-Date cards and discounted invitations.

UPrinting
Use this link for Free Shipping on Poster Printing.
Use this link for Free Shipping on Vinyl Banners.
Use this link for Free Shipping on Canvas Printing.
Use this link for Everything else.