Amy : http://www.oozak.com/, they have great prices and selection along with super quick shipping . And Free shipping for orders over $50.
PAPER: As paper goes, I use mostly Copic X-Press It, I get nice vibrant colors with it and because it is a bit thinner it is easier to fussy cut the image out. I also like the results I get with Paper Trey Ink white cardstock. I tried the Neenah and didn't like how it bled and even seemed to smear the ink of my stamped images in some places. But again, this is just my experience and preference for how I color =)
Kim: I originally bought a large 72 marker set from ebay, I found that http://www.refuelled.com/ and http://www.artifolk.co.uk/ has the reinkers and a larger range of colours! If you take a look at this chart I have set D and set B, also http://www.copicmarker.co.uk/ is quite near where I live, I just haven't had the chance to visit... yet, LOL!
This is my copic collection, hoping one day to have them all (we can dream hey?)
I get mine from here and it's not branded but what I like to look for is not too high gsm so it doesn't take all the ink from my copic pens but also a good grade so it's not at all flimsy. Ideally acid free, and smooth surface. My choice is Exclusive white card - A4 - 250gsm - CW309. I buy a bulk lot and share it with my mum to keep cost down and it's fantastic card for the card bases too, hope it helps.
I tend to buy most of my markers from http://www.artifolk.co.uk/ - they dispatch quickly and have a wide selection of all the markers and refills.
I like to play around with different papers, but for the most part I use Splendorgel Extra White 270gsm from Century Paper.