I've noticed that I tend to request more books from paperbackswap.com but my books are more often requested from bookmooch.com. Paperbackswap gives you points for each referral that you bring to the group. You get two credits per new recruit. It does not offer additional points for each book that you list. In contrast, bookmooch offers 1/10th of a point for each book that you list but does not offer any referral points.
Bookmooch seems to be stricter about its wishlist and inventory. You must send books that are posted in your inventory and you must request the books on your wishlist that become available. Paperbackswap isn't as strict about these items, but it is stricter about sending the books within a short period and a fuller description of requestor restrictions and the way that the books are packed, listed and sent.
I love using both groups - it makes it possible to recycle books that I'd like to read once and don't have space to keep in the apartment. I can also request books and have them sent to friends and family members in the US. Bookmooch has the added advantage of having a global reach - it allows you to request books from people outside the US and you can opt to send the books outside the US for a greater number of points. Check both sites out!
Craigslist is a good way to sell used items within your neighborhood. Be careful about scheduling appointments and giving out personal details - some people have used fake postings to lure victims out with cash and then robbed or mugged them.
If you don't have time or the patience to sell the items, you can choose to give away things through the different Yahoo freecycle groups. It's a great site and I've benefited from some generous posters/freecyclers. We've gotten a new paper shredder, blender, a baby car seat, and numerous books (law, fiction, mysteries, etc.)
Now that we've moved to Brooklyn, we noticed that people leave items on their stoop for neighbors to take. Just while having coffee on 9th Street and 6th Avenue, a man brought down a microwave and toaster and put them on his stoop. Less than five minutes later, a woman put the toaster on top of her stroller and took it home! They bypass the hassle of posting and scheduling pickups on freecycle and still share with the neighbors.