If you are using MacVim or a terminal that supports transparency (e.g. Iterm) I suggest you set your background transparent and you will be able to see the cheat sheet while editing. Set it something between 10-20 percent and you should be fine. For example in MacVim:
OmniGraffle files are included if you feel like customizing this to your own vim colorscheme.
Thanks to @EspadaV8 there's a dark version of this wallpaper now as well.
There is also a version with a 'real' background based on tremblingpixels' breathe wallpaper now:
We also have a version that preserves the gradient of the original, but changes the color to a nice soothing blue: