I belong to these websites which allow me to safely share what I have with others and in so doing help keep costs down and reduce our impact on the environment.
We can, of course, also benefit from these wonderfully generous people by receiving hospitality as well as giving it. Both parties should get something out of it, and put equal effort in.
They are vouched for, safe, friendly and a great way to cheaply travel, meet local people and avoid rip-offs.
I am also a big fan of hitch-hiking (which is safe in the UK) and hostel accommodation (like YHA.ORG.UK) which allows me to self cater yet move on every day. This really keeps costs down (as eating out is so expensive / not so healthy) and increases flexibility.