Well, if you're thinking they should be worth something, you could try www.24carat.co.uk. I haven't any experience of them, but their FAQs page (http://24carat.co.uk/coinquestionstheyaskus.html) suggests they may buy old coins off you. Obviously, you'd have to foot the bill for postage, which may be more than you'll get for them...!!!
Otherwise, you could do the charitable thing. The RNIB collects coins - gather them together and call 020 7388 1266, who will give you details of your local RNIB office. Oxfam also collects coins, and you can drop bags of coins into any Oxfam branch. I'm not sure how they benefit from the collections, although it seems they do get something for the coins they collect.