vi cheat sheets   (link)

http://jmcpherson.org/editing.html
efficient editing with vim. a very good guide to vim.

http://www.georgehernandez.com/xComputers/LinuxUNIX/vi.htm
common commands reference

http://york.gose.org/wiki/index.php/Advanced%20VI
more advanced vi topics like screen splitting, etc

http://www.linuxpowered.com/html/tutorials/vi.html
centering cursor on screen, etc

http://www.rayninfo.co.uk/vimtips.html
lots of random tips

http://heather.cs.ucdavis.edu/~matloff/ProgEdit/ProgEdit.html
programmer-oriented vim tips with screenshots