Using ESXi 4.1:

vm705:~ # esxcfg-vswitch --add-pg=vlan301 vSwitch0           
vm705:~ # esxcfg-vswitch --vlan=301 --pg=vlan301 vSwitch0

And this was to move a bunch of VLANs from one vSwitch to another:

vm705:~ # for i in `seq 221 235`; do esxcfg-vswitch -D vlan$i vSwitch0; done;
vm705:~ # for i in `seq 221 235`; do esxcfg-vswitch -A vlan$i vSwitch1; done;
vm705:~ # for i in `seq 221 235`; do esxcfg-vswitch -p vlan$i -v $i vSwitch1; done;