Riding boots are hot right now, which means there are a lot of choices available. I prefer a simpler boot, without a lot of extraneous buckles, straps or hardware to look dated in a year or so. Here are some options, all under $200.
AK Anne Klein
A hacking jacket is another horsey item that translates well to a classic work wardrobe. Ralph Lauren made his bones on equestrian-inspired wear, and hasn't lost his touch.
Scarves can also be easily incorporated into one's regular wardrobe. To keep from looking like the Queen Mum, pass up the elaborate knots and throw over your shoulders casually, with a "this-old-thing?" insouciance.
Or, the Mother of Them All, Hermés.
I know jodphurs have made an appearance on the runways recently, but frankly, that's one item I'd skip. Not only are they rarely flattering, but they're tough to wear without looking a tad...costume-y......or worse.