Here's a way to get info on currently running processes and sort by Working Set size
Get-Process | Sort-Object -Descending WS
Assign that output to a variable and it'll give you an array of the results, then you can just write out the first member of the array (which in this case will be a System.Diagnostics.Process object).
$ProcessList = Get-Process | Sort-Object -Descending WS
Write-Host $ProcessList[0].Handle "::" $Process.ProcessName "::" $Process.WorkingSet
Here's another quick and dirty script to dump a few items of data from the list of currently running processes using WMI's Win32_Process provider:
$ProcessList = Get-WmiObject Win32_Process -ComputerName mycomputername
foreach ($Process in $ProcessList) {
write-host $Process.Handle "::" $Process.Name "::" $Process.WorkingSetSize
}
That'll list the PID (handle), process name and the current working set size. You can change that up using different properties of the WMI Process class.