You can look up your quilting books on Amazon to see the "Used - Like New" prices. You can decide if it's worthwhile to sell them there. It's pretty easy to list them, but there tends to be a lot of competition so they may not sell.
Magazines are expensive to mail because they cannot be sent media rate (because of the advertisements in them). You can try eBay or the SewItsForSale group on groups.yahoo.com, but I'm not sure how well they sell. I ended up giving mine to thrift shops and the local library. The library might keep some of them, but mostly I think they sell them at their annual used book sales.