You can get memory using following command, but I bet it's not you expect.
# xe vm-list params=memory memory (MRO) : memory (MRO) :
More interesting values you can get using params=all. The problem is that you will get hundreds of other values too. This is not helpful, but of course grep can help us:
# xe vm-list params=all| grep memory memory-actual ( RO): 536870912 memory-target ( RO):memory-overhead ( RO): 6291456 memory-static-max ( RW): 536870912 memory-dynamic-max ( RW): 536870912 memory-dynamic-min ( RW): 536870912 memory-static-min ( RW): 536870912 recommendations ( RO): memory (MRO): memory-actual ( RO): 500170752 memory-target ( RO): memory-overhead ( RO): 15728640 memory-static-max ( RW): 789839872 memory-dynamic-max ( RW): 500170752 memory-dynamic-min ( RW): 500170752 memory-static-min ( RW): 395313152 memory (MRO): memory-actual ( RO): 1073741824 memory-target ( RO): memory-overhead ( RO): 10485760 memory-static-max ( RW): 1073741824 memory-dynamic-max ( RW): 1073741824 memory-dynamic-min ( RW): 1073741824 memory-static-min ( RW): 1073741824 recommendations ( RO): memory (MRO):
It's not so useful yet, because we have only memory related value, but we don't know relation between them and VMs. Luckily, we can very easily extend our grep.
# xe vm-list params=all| grep "label\|memory" name-label ( RW): at10 memory-actual ( RO): 536870912 memory-target ( RO):memory-overhead ( RO): 6291456 memory-static-max ( RW): 536870912 memory-dynamic-max ( RW): 536870912 memory-dynamic-min ( RW): 536870912 memory-static-min ( RW): 536870912 recommendations ( RO): memory (MRO): name-label ( RW): Control domain on host: dt33 memory-actual ( RO): 500170752 memory-target ( RO): memory-overhead ( RO): 15728640 memory-static-max ( RW): 789839872 memory-dynamic-max ( RW): 500170752 memory-dynamic-min ( RW): 500170752 memory-static-min ( RW): 395313152 memory (MRO): name-label ( RW): at11 memory-actual ( RO): 1073741824 memory-target ( RO): memory-overhead ( RO): 10485760 memory-static-max ( RW): 1073741824 memory-dynamic-max ( RW): 1073741824 memory-dynamic-min ( RW): 1073741824 memory-static-min ( RW): 1073741824 recommendations ( RO): memory (MRO):
Now we know that the at10 has 0.5GB, the at11 1GB and the dom0 might have between 386 and 771 MB.
Summary
Of course similar construction in grep query might be use for other variables.E.g. to have the list of live VMs try:
xe vm-list params=all| grep -i -E '(label|\s+live)'