Donate Your Old Stuff - Or Get Other People's Donated Stuff
I think Freecycle was mentioned here before. A second site is Excess Access.
I've put the Excess Access info here:
"First, you provide your location, then you post your items or wishes. We do all the matching in-house 24/7. Nonprofits/recipients are alerted, by email, to donations nearby that match their wishlists. We serve throughout US, Canada and beyond.
Recipients reserve items of interest. Donors have the right to cancel or confirm reservations.
Recipients are responsible for pick-up (unless the donors urgently want to drop-off). Excess Access provides follow-through emails to make the process easy. And we send tax-deductible receipts/ Thank You letter paperwork for the nonprofit and donor once we're notified pick-up / drop-off has occurred.
Recipients: can update / edit / add / delete wishes at any time.
Donors: can update / edit / add / delete donation postings at any time
We have over 81% successful matching rate, but can't offer any guarantees except that we try our hardest to help you and our environment by keeping useful materials out of garbage dumps and getting them into the hands of those in need."
You can also sell or give away your stuff at Craigslist.