If you're looking for decent storage boxes for slot cards or room keys I've found a great box from U-Line (Catalog# S-9847) that is actually a business card literature mailer. It's heavy gauge white cardboard that measures 7" x 3-5/8" x 2-1/8" inside and easily holds about 200-220 slot cards or similar.

I actually tried listing a few on eBay and got a lot of inquiries but the shipping costs on small quantities was pretty prohibitive. If you buy direct from U-Line the boxes are sold in multiples of 50 for something like $17 plus shipping & sales tax. Larger quanties of 100, 300 or more bring the cost down considerably. I have some left if anyone would want to trade some cards for boxes maybe we can work something out.

By the way, U-Line has some othe larger (i.e. longer) boxes for business cards but they're not as heavy cardboard and/or aren't as easy to use due to their construction.

Their website is: http://www.uline.com/