Here in the UK we are entering into a bank holiday weekend, the second this month. It seems rain has been forecast, this is to be expected. So, if you are stuck indoors this weekend, here are few things to occupy your time.
You could take a look at Project Gutenberg, a database of free books. Unless, your ancestors were highly noted, you probably won’t find anything which mentions them directly – although it’s always possible – but it is still a good place to find historical and geographical information.
Pay a visit to Wikipedia to find free images or maps. The maps seem to be mostly from the US, but other areas are covered too. The images cover a wide range of themes including some posters from World War 2.
Make specialised searches of Google. Not all the options will be of use to family historians, but many will, especially the translated and book searches. Once you have done that, find out how you make your ordinary searches more productive.
Finally, why not add some content to the National Archives wiki, a collaborative effort to provide information which isn’t currently in the archives.
Have a lovely weekend, wherever you are!
Kate's Family Tree 
Great post for rainy day searching. My family was nobility and have search, read many sites you mentioned like Project Gutenberg.