Most reputable companies include an 'unsubscribe' link in their mails. So the first thing to try is clicking that link.
(NB: Never click an 'unsubscribe' link in random spam, from people who've you've never had any contact with. It only serves to show that your email address is valid and it will result in you getting lots more spam. Only use 'unsubscribe' when the mail comes from a reputable company, like Amazon).
Otherwise, using Mailwasher and a combination of 'confidential' and 'disposable' email addresses should help. See my post here for details:
http://www.theanswerbank.co.uk/Technology/Ques tion624424.html
Chris