VI3 Reference Card
Never leave home without it.
No, it's not an Amex card, it's the VI3 Reference Card written by Forbes Guthrie. A lot of things on this little gem pop up or are useful in the VCP exam and day-to-day it's come in handy a number of times.
I'll try and keep a link to it in my useful links sidebar but it's well worth bookmarking it yourself.