Where can I buy a deck of personalized cards?
I've had great experiences with Printer's Studio.


You can have anything from a custom back on standard playing card fronts to completely custom fronts and backs that are different for each card.
Good interface for building these decks.
While the images you submit must have a bleed, the jobs I submitted were spot-on.
No minimum order size (though you get discounts for buying in bulk).


Tips:


Don't order without a coupon. You can always get a deal. At the very least, sign up for the mailing list to get $10 off, which will cover the shipping. (The best I've seen was early in the new year where they had a deal for 15% off and free shipping!)
You might be able to save a buck by going to the Canadian portal. The prices of items are the same as the US portal, but the Canadian dollar is weaker. The company is based in Hong Kong.
If you want cards that are perfectly flat, go for the linen instead of the standard. Both types are high quality. (I have no experience with their "plastic" cards.)