Use them as a raised bed. Fill the centre with soil and plant some veggies in them or flowers.

you could 'google' Bob Flowerdew from gardeners question time-- he uses all kinds of things to grow-- I seem to remember him growing potatoes and as they grew instead of ' earthing up 'conventionally would add another tyre and more compost!

I remember him doing that PamG. You could also grow something climbing like sweet peas round the outside to hide the tyres if you don't like the look of them. A dwarfer s.pea probably.

Bob Flowerdew's method seemed to involve some pretty tricky and possibly dangerous work removing the inner 'lip' to make a straight tyre wall inside. I wouldn't fancy trying cutting through the steel wire or whatever there to do this. But if you don't, you have that huge 'cavern' area inside the tyre which is difficult to fill with compost and which fills with water, in my experience.
You could try lining the inside with black polythene or something, but much though I don't like throwing things away, I prefer to steer clear of tyres nowadays.

I think he filled the cavity with straw because I remember a GQT from a listener who thought he meant growing in straw ( no compost) and Bob's words failed him as he realised she hadn't used compost at all !