Need help heading to Open Source

Up until this point my career has been in VMS Systems Management. Due to losing my position, and a scarcity of VMS sites, I am trying to restart my career with a focus on Linux, and the open source tools, and utilities. I would love to become involved in web development and support, e-commerce, and architecture/infrastucture using Linux, and open source.

Here is my question:
Other than learning the basics of Linux sys admin, what are the most current and prevalent open source software packages, and tools which are musts to learn in order to compete for the job I want these days?