- The Brittle Bone Society
- Great Ormond Street Hospital (in London, for children) has a charity. Link. They accept stamps, postcards, and through another organisation, printer cartridges.
- Hearing Dogs for Deaf People
- Macmillan Cancer Support
- Royal National Institute of Blind People (RNIB)
Many others collect stamps. Some are listed in the directories below, but in time, I hope to bring you the charity's own webpage link.
- Used Stamps For Charity
- Waste Connect
- www.xchange-master.co.uk/charities/4578336972 is a middle-company working with various charities accepting donations of foreign/obsolete/out-of-circulation currency, and stamps.
- www.recyclingforgoodcauses.org/stamps/ is also a middle-company working with various charities.
- Oxfam Canada (incidentally, although Oxfam is also in the US, I can't find mention of them wanting stamps).
- The Veterans National Stamp and Coin Club
- Holocaust Stamp Project - They'll even take damaged stamps.
- Sisters of the Holy Cross
- American Philatelic Society - uses stamps for educational purposes
- The Postal History Foundation - uses stamps for educational purposes
- GiveNow is a directory of some charities/organisations accepting stamps (they also have options of giving other items).