I came across a neat service named Cryocopy earlier today. What it essentially does is mimic the service provided by archive.org except for the fact that Cryocopy does it on demand instantaneously and saves a screenshot to boot.
CryoCopy is a web archiving service that allows manual caching of Internet pages, fully saving them both in HTML and in bitmap (PNG) format. This is done almost instantly upon request, not days or weeks apart, like with other services.
Aside from using it as a tool to simply backup pages, CryoCopy also comes in handy when you want to save a page containing sensitive information before it has a chance to be removed or updated.
For instance, if you spot some "leaked" info, or copyrighted material illegitimately published on a page, and you think it will be taken down in no time, you can save the exact copy of that page, as it appears at that moment.
Other uses may include making several copies of the same page over a period of time, in order to follow its evolution; or saving a page from an overloaded server that looks like it might come crashing down any moment; etc.