Hi,
For the Sup720, you can choose from the following IOS versions, which support IPv6 and they are the latest in each train. I would recommend SXI6.
12.2(33)SXH8a
12.2(33)SXI6
12.2(33)SXJ
On Sup2 / MSFC2 engines IPv6 is only supported in software (i.e. no hardware support for ipv6) and it needs 12.2SX image at least. The 12.2SX images also require that you have 256MB of RAM on both the SP and RP.
For MSFC2 the latest version is 12.2(18)SXF17b.
For specific IPv6 features, please visit the Feature Navigator on the following link:
http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp
And look at the IPv6 roadmap as well:
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-roadmap.html#wp1030415
Best regards,
Andras