I see that you have added some References and Tools :)
Something else worth knowing (and I haven't seen it publicised recently) is the free online access to Oxford University and other books through local libraries. There is information about the national agreement (running until about March 2008) here
By using the membership number from my local library I now have access at home and free to the OED, DNB, the Times from 1785 to 1985 and lots more. Check the website of your local library for 'online resources' or similar to see what you can get access to.