The Mutr.co.uk site is definitely worth a visit and it’s a great site to order stuff from if you live in the UK.
I have used them 2 times so far for various bits and pieces and I have been very satisfied.
One of their best sellers, the polymorph, is already one of my favourite plastic: you put a spoonful of these white bits of plastic in a container; you pour some hot water in it, and then all of a sudden, you can actually change the shape of the plastic as if it was plasticine. Then, when you are done, you let it dry and you get a very hard plastic. And then you can melt it again!
For some ideas of what you can do with it, go to instructables. It will cost you approx £16 (vat included) to buy a kilo of polymorph at MUTR; it will cost you approx £33 to buy a kilo from Maplins…
I also really like their K’lik system; it’s a great prototyping system and it’s very very cheap!
Overall, Mutr.co.uk offers great materials for really low prices.
I highly recommend them and no, I do not work for them! 🙂