I have a lot of small digital memory cards.  I don't want to lose
them, and I prefer to have them close by in case I need them.   I
never want to be without additional memory in case the card in my
camera fills up.  Is there a product out there that can help me better
manage my memory cards?

Use Froogle

If in USA -
http://froogle.google.com/froogle?q=memory+card+holder&btnG=Search+Froogle
OR
http://froogle.google.com/froogle?q=memory+card+wallet&btnG=Search+Froogle

Hi Kelly,

I saw this product called the iPorter.  It holds 3 memory cards.  The
cool thing about this holder is it fits on your key chain or could
clip to your camera bag, so it would be perfect for what you want to
do, which is keep your cards handy and close, prevent loss, and
protect the cards while they are not in use.  A company called
ePorter, Inc. holds the rights to market them and is selling them on
their website.  You can see the company website at
http://www.eporterinc.com.  Just click the "Buy Now" link and you are
taken to their online shopping cart.  According to ePorter, Inc., the
case can hold SD cards, MMC cards, Memory Stick Duo, xD cards,
mini-SD, Reduced Size MMC, and other similar sized cards.  You can
also see what others are saying about them, by reading reviews written
about the iPorter xSD.  They are selling their cases in a two-pack for
$9.95.

There are several card cases on the market.  You could try doing a
search for memory card case or memory card holder.  I did find many
cases out there, but most of them were soft or if they were more rigid
so that they could better protect your cards, then they usually were
restricted to one card type.  I looked at the iPorter mentioned by
jporter67 and they seem to offer a lot of flexibility that is not out
there in the other cases.  The reviews were rather positive.  One
attractive featuer I noticed is the case is small compared to other
holders, and so it is easier to pack around.