Which of the following methods is best for redundancy in a Cisco 6500?
- Two Cisco 6500 chassis each with a single Sup720 and other modules.
- One Cisco 6500 chassis with two Sup720 modules and two of each of the other modules.
Depending on what Sup720 you have (or plan to buy) you could consider a 3rd option. With the VSS-720-10G Supervisor you can "cluster" two 6500 boxes to appear as one single entity with very fast failover between the two, you need decent 10gig line cards for this though, x6708 typically. Each chassis can have one or two supervisors for redundancy.
There is quite a long list of pros and cons for this type of setup, best is to google and speak to your Cisco sales rep about the options.
Also worth keeping in mind that the Nexus is the next generation switch for datacentre deployments, if you don't need the services offered on the 6500 (6500 = services and Nexus = performance) you might want to consider Nexus instead. On high density 10GE the Nexus is a lot cheaper.
This needs more information, however I would be inclined to go for 1, Two Cisco 6500 chassis each with a single Sup720 and other modules.
My reasons being, you can then locate the devices in separate locations, should one location "go dark", the other should continue to run with the separate hardware.