When a friend or client asks me about area rugs, usually the first words out of my mouth are "seagrass" or "sisal". Now, I am far from the "neutral" or "beige" school of decorating, but even my own home is filled with seagrass rugs.
First of all, they are affordable. I'd sooner spend a few hundred on a natural seagrass rug than try to find an inexpensive poly or olefin wannabe Oriental rug. They also help bridge styles (see "Juxtaposition" below). Say you inherited (or purchased secondhand) some more formal wood pieces but your style is a bit more casual; or, in the case of some clients I had, did the whole chintz/English garden living room but now want to break up the formality somewhat. Introducing a natural texture like sisal or seagrass is a simple, inexpensive way for your room to say "don't be afraid, come on in, I'm not as serious as I look." Now, I happen to love the way seagrass feels underfoot, but, if you find it too scratchy or have a baby that crawls around, there are some options using wool/sisal blends, and yes, even poly sisal which can be hosed down or even used on a porch or deck.
I have found great prices on sisal rugs at Overstock.com, Homedecoratorsoutlet.com, Restorationhardware.com and at Ikea.