I don't know anyone who doesn't enjoy shopping in Paris. It's a rewarding experience on so many levels. Personally, I love the specialty boutiques and the quality of the merchandise found within.
For the equestrian, I recommend Guibert located at 22, avenue Victor Hugo. Guibert offer everything from saddles, blankets and riding boots to silk scrarves, wallets and gloves. Several years ago, I purchased an all-weather riding jacket. To this day, whenever I wear it, someone asks me where I purchased it.