Helpful Textbook Online Resource for Economics

Estrin & Laidler: Economics:

http://wps.pearsoned.co.uk/ema_uk_he_estrin_microecon_5/98/25124/6431792.cw/index.html

Begg, Fischer & Dornbusch:

http://highered.mcgraw-hill.com/sites/0077107756/student_view0/index.html

Lipsey:
I find this to be the most extensive and useful online resource, check this out

http://www.oup.com/uk/orc/bin/9780199286416/