http://www.greatbabyproducts.com/Twins_s/26.htm Offers a 30% discount to parents of twins and triplets.

 http://www.twinstuff.com/store/catalog/  Shopping for twins and other multiples.

http://www.twinshelpstore.com/  Clothing for twins, focuses primarily on matching clothing.  Also has links to MANY other multiple/based websites.

http://www.tobuytwo.com/ An auction website for multiples