One of the best link collections i ever saw related to vSphere 4.1, all the study materials are there for you to start playing with vSphere 4.1.
Eric Siebert done a good job to contribute this much resource in one piece
These are some of the best VCP4 Study Materials from VMware and other blogs; this can be useful for reference and study for the VCP4 certification.
VMware Official Documentation for vSphere
vSphere 4 card and esxtop precis has been recently updated in vreference by Forbes Guthrie, This is one of the useful reference guide for the VMware administrators.