oniomania - an uncontrollable urge to buy things
Jackie > I think this is commonly known as shopping addiction.

I agree with Jackie about oniomania.
"Retail therapy" though has a different meaning to me. It has more to do with shopping than buying. For a woman, it's getting out of the house, away from responsibilty for a few hours.
Men do not seem to understand that when we admire an extravagant dress, it is not the dress we want but an invitation to a place or party that calls for wearing such a dress. Daydreams are what retail therapy is all about.
Now, is there "catalogue therapy?" she asked, browsing through the latest catalogues from the Smithsonian and from Levingers...