Though I tend to find it easier to search for books through Google for the internet archive, I want to highlight it here because I have found a few books through the site that have been very useful. You can view the book in a variety of formats, some easier to to text search than others.
Connected Histories has several databases, a mixture of free and subscription, that you can search in one go for British history sources, 1500-1900. It has quite a few resources that will help the researcher in the area of context when researching your own history.
I also wanted to thank all the people who have stopped by my blog in the past few days from geneabloggers. Thanks for the welcome!