The free ADVIS Mailing List web part can be placed on a site/area together with a contacts list view. It allows you to quickly send an e-mail to all currently shown contacts (filtered or unfilterd) in the connected list view. You can select if you wish to see [mail to...], a [cc to...] and/or a [bcc to...] button.

You can also use MailingList to quickly and easily send an e-mail to all members of the current site or subsite.