[x2drich2000]

The last set of boxes I got were these http://www.ebay.com/itm/380719017445...%3AMEBIDX%3AIT

I generally use these for anything over $100 or more than 2/3 graded cards.
I make a sandwich with two extra pieces of cardboard cut to just fit inside the box but still slightly large than the graded card case. Graded cards have just a little wiggle room. You can easily ship multiple cards by first class without a problem. I don't recall how many cards exactly you could put in before you go over the weight limit for first class, but I know if your only shipping 3-5 graded cards it will likely only cost you $2.77 (through ebay/paypal multi-order shipping) and therefore being able to cut the cost of shipping in half compared to a small flat rate box.

DJ