I sell a lot of card sets and I get my packaging materials from
www.clearbags.com - I get the soft fold clear boxes for card sets
FB27 - 4 1/2" x 13/16" x 5 7/8" (fits 6 bulky (ribbon, brads, etc..) cards and envelopes or 8 non-bulky)
FB3 - 4 1/2" x 5/8" x 5 7/8" (fits 6 non bulky cards and envelopes)
I also get the card sleeves (bags with no flaps)
4 5/8" x 5 3/4" (117x146)
Crystal Clear Plastic Bags with No Flap and No Adhesive - Fits a single A2 or 5 1/2Bar (4 3/8 x 5 3/4) envelope and card
#B54NF
Their envelopes are pretty good too. I have gotten the Ashley envelopes before in Bright white and Natural (goes great with SU vanilla) - be sure to look at the prices - the more you buy the less it costs per piece - so you can get a lot more for just a few $$ more...
I have also bought Checkbook holders and book mark sleeves from them
This site is wholesale so you need a minimum order of I believe $40 in order not to get hit with a service charge - the shipping is a little pricy (my last order was about $140 and shipping was almost $20) - but I usually wait until I have a fairly large order so when you break down the cost of shipping over each item it isn't all that bad