There's an old joke in the printing business that went something like: "good, cheap and fast - pick any 2". I have had great success with a company called Vistaprint, having ordered full color business cards, letterhead and postcards from them. They often have specials that make their printing pretty cheap, and yet the quality is excellent. The only "trick" is to order far enough in advance so you don't have to pay for expedited shipping. I recently ordered 100 postcards for $4.99 and the minumum shipping was 5.99 - if I wanted the postcards within a week I would have had to pay $18 or something like that so I didn't - and the postcards still came in just about a week. They look GREAT, just like the original Photoshop file! So, Vistaprint is good, fast AND cheap!
They're always running specials
I highly recommend them.