printerstudio as before is highly recommended. I'd upgrade to the linen cards though as the basic cards can get scratched quite easily.
also
makeplayingcards.com is slightly more expensive for the same thing (unless you want thousands)
I've bought from printer studio loads of times and they are really easy to use. They have a really good online card creator. All you need to do is upload the images and put them in the order you want and they are sorted.
edit #1: Also sign up to their newsletter if you aren't in a hurry as they always have special deals going.
edit #2: ALSO if you are after irregular sized cards there is a prototyping company (who's name I will have to find out when I get home) who makes different sizes to order. It's more expensive but you get what you want and can also actually make boards from it too. Based in the USA.
edit #3:
found it
http://www.printplaygames.com/