There are multiple way to do this, depending on your budget, capabilities on the edge of DC/HQ, scale etc etc.
L2tpv3 and pseudowire methods (VPLS?) are OK for smaller deployments (and some pretty big ones ;])
OTV would be mentioned typically whenever someone wants to extend L2 between DCs.
Have a look here:
http://www.cisco.com/c/en/us/products/collateral/data-center-virtualization/data-center-interconnect/white_paper_c11_493718.html
http://www.cisco.com/c/en/us/products/collateral/switches/nexus-7000-series-switches/white_paper_c11-644634.html
The best, if you have the time, is sit down with your sales/AS rep with your topology and goals.