ok- I thought I saw this somewhere-LOL!
Lisa (Leewinz) recommends whcc.com see the 4th question from the bottom here:
http://whcc.com/faqs.html
Here's the pricing page:
http://whcc.com/output_cards.html 4x8's are 45 cents including envelope- not bad
The site is a little difficult to navigate because it's hard to see where the links are, but they sound like a very professional company!
This sounds like a good place for 4x8's, but I think winkflash is cheaper for the standard sizes.