http://www.comeaucomputing.com/tryitout – online C++ compiler, declared by authors to be very standard-compliant. interesting reference point if in doubt i think.
http://hgbook.red-bean.com/hgbook.html – Mercurial is a distributed source controll system written in Python. here is link to e-book (htmls) describing it in detail.
http://no-spam.ws – site that creates e-mail addresses on-the-fly - no registration, to passwords. perfect for “give e-mail address to register”-and-forget pages.